Journalist Napoleon Hill set out to uncover the key to wealth around 80 years ago.
He studied more than 500 self-made millionaires over a span of 20 years and his research culminated in what would become a timeless personal finance classic, “Think and Grow Rich.”
In addition to boiling down the “secret” to building wealth in his book, he revealed 30 “major causes of failure” that hold many of us back from getting rich.
Here are 19 that are still relevant today:
'There is no hope of success for the person who does not have a central purpose, or definite goal, at which to aim,' Hill writes.
You have to want to aim above mediocrity, Hill says: 'We offer no hope for the person who is so indifferent as not to want to get ahead in life, and who is not willing to pay the price.'
Wealth doesn't simply appear. You have to work toward it with patience and persistence. A good starting point is to invest your money (the earlier the better), and let the power of compound interest build your wealth. It doesn't take much time or effort, but it does require action on your part.
A college degree alone won't cut it. Knowledge is only potential power, and it will not become useful or lead to great wealth unless it is organised and applied to life, Hill emphasises:
'Education consists not so much of knowledge, but of knowledge effectively and persistently applied. Men are paid not merely for what they know, but more particularly for what they do with that which they know.'
Make it a priority to constantly learn new things and challenge your mind. There's a reason that many of today's successful and wealthy people are voracious readers.
'Discipline comes through self-control,' Hill writes. 'This means that one must control all negative qualities. Before you can control conditions, you must first control yourself ... If you do not conquer self, you will be conquered by self.'
When it comes to getting rich, the most basic formula is: Save more, spend less. It's a simple concept, but spending less requires discipline. Learn to recognise and manage overspending triggers if you want to start accumulating wealth.
'No person may enjoy outstanding success without good health,' Hill writes. It's no coincidence that many millionaires make time in their schedules to exercise.
If you haven't mastered your body, the good news is that many of the causes of bad health -- overeating, negative thoughts, and lack of exercise -- are completely under your control.
If you're pressed for time, try this seven-minute workout you can do at home.
Hill calls procrastination one of the most common causes of failure: 'Most of us go through life as failures, because we are waiting for the 'time to be right' to start doing something worthwhile. Do not wait. The time will never be 'just right.'
'Start where you stand, and work with whatever tools you may have at your command, and better tools will be found as you go along.'
If you want to build wealth, start today. Pick up a personal finance book, listen to a podcast about money management, form a financial plan, or contribute toward a 401(k), Roth IRA, or traditional IRA.
'Most of us are good 'starters' but poor 'finishers' of everything we begin,' Hill writes. 'People are prone to give up at the first signs of defeat.'
Don't stop until you get what you want. The most successful people tend to have dealt with, and have overcome, failure. 'I've learned that it doesn't matter how many times you failed,' billionaire Mark Cuban told Smart Business. 'You only have to be right once. I tried to sell powdered milk. I was an idiot lots of times, and I learned from them all.'
'There is no hope of success for the person who repels people through a negative personality,' Hill writes. 'Success comes through the application of power, and power is attained through the cooperative efforts of other people. A negative personality will not induce cooperation.'
If you want to grow rich, positive emotions must dominate negative ones, Hill emphasises. He was on to something: Today, research shows that positive, happier people are more likely to perform better at their jobs and are less likely to be unemployed.
'Analysis of several hundred people who had accumulated fortunes well beyond the million-dollar mark disclosed the fact that every one of them had the habit of reaching decisions promptly,' Hill writes.
On the flip side, 'People who fail to accumulate money, without exception, have the habit of reaching decisions, if at all, very slowly, and of changing these decisions quickly and often.'
Decisiveness is not just a trait of the wealthy but one of the most important qualities a leader needs to possess. At the end of the day, making a bad decision is better than making no decision at all.
Hill highlights this as one of the most common causes of failure. 'Unless this relationship is harmonious, failure is likely to follow,' he writes. 'Moreover, it will be a form of failure that is marked by misery and unhappiness, destroying all signs of ambition.'
His claims are backed by research. One study, by Brittany C. Solomon and Joshua J. Jackson of Washington University in St. Louis, suggests that having a conscientious spouse can boost your salary by $4,000 a year.
'The person who takes no chances generally has to take whatever is left when others are through choosing,' Hill says. 'Over-caution is as bad as under-caution. Both are extremes to be guarded against. Life itself is filled with the element of chance.'
When it comes to managing your money, it can be tempting to let your savings sit 'safely' in your bank account to avoid feeling repercussions from another stock market crash. However, investing your money is how you'll make more of it.
You'll want to do so wisely, of course, and a good starting point is to look into low-cost index funds, which Warren Buffett and other investing experts recommend.
'One should use great care to select an employer who will be an inspiration, and who is, himself, intelligent and successful,' Hill advises.
This concept extends beyond your boss and associates; it is also important to surround yourself with talented and driven people outside your work. Hill calls this creating a 'Master Mind' group.
We become like the people we associate with, which is why the rich tend to make friends with others who are rich.
'No man can succeed in a line of endeavour which he does not like,' Hill writes. 'The most essential step in the marketing of personal services is that of selecting an occupation into which you can throw yourself wholeheartedly.'
If you're not sure how to have this conversation with your boss, check out advice from Richard Branson, Robert Herjavec, and six other super-successful people.
'The 'jack-of-all-trades' seldom is good at any,' Hill writes. 'Concentrate all of your efforts on one definite chief aim.'
If you want to get rich, you need to become obsessed with this desire, Hill says: 'Wishing will not bring riches. But desiring riches with a state of mind that becomes an obsession, then planning definite ways and means to acquire riches, and backing those plans with persistence which does not recognise failure, will bring riches.'
'Without enthusiasm one cannot be convincing,' Hill writes. 'Moreover, enthusiasm is contagious, and the person who has it, under control, is generally welcome in any group of people.'
Billionaire Donald Trump echoed this thought nearly a century later, when he stated, 'Without passion, you don't have energy; without energy, you have nothing. Nothing great in the world has been accomplished without passion!'
'The person with a 'closed' mind on any subject seldom get ahead,' Hill says.
You must be willing to continually collaborate with others, imagine new ideas, and innovate. The wealthiest and most successful people think differently.
To start thinking differently, do different things, expose yourself to different people, and value other ideas, says John C. Maxwell in his New York Times best-seller, 'How Successful People Think.'
'Most people lose their positions and their big opportunities in life because of this fault than for all other reasons combined,' warns Hill.
Building an empire takes people skills and charm just as much as it does strategy.
Mark Cuban put it bluntly in an Entrepreneur article about the keys to being successful in business: 'People hate dealing with people who are jerks. It's always easier to be nice than to be a jerk. Don't be a jerk.'
While dishonesty may grant you a few victories in the short term, it's not a sustainable way to attain success or accumulate wealth, Hill warns.
'There is no hope for the person who is dishonest by choice,' he writes. 'Sooner or later, his deeds will catch up with him, and he will pay by loss of reputation, and perhaps even loss of liberty.'
Beware of the 'uncontrolled desire for 'something for nothing,'' writes Hill — or, 'get rich quick' schemes, such as gambling, excessively playing the lottery, or trying to time the market.
'The gambling instinct drives millions of people to failure,' he writes. 'Evidence of this may be found in a study of the Wall Street crash of '29, during which millions of people tried to make money by gambling on stock margins.'
Investing is a long term game. As Warren Buffett says, 'It's pretty easy to get well-to-do slowly. But it's not easy to get rich quick.'