Napoleon Hill has a great list of reasons behind failure in his book "Think and Grow Rich".

Here is that list (and modern translations by us if necessary)

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  1.UNFAVORABLE HEREDITARY BACKGROUND.  (lack of intelligence) 
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• 2. LACK OF A WELL-DEFINED PURPOSE IN LIFE.  (lack of an actual, attainable goal.)
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• 3. LACK OF AMBITION TO AIM ABOVE MEDIOCRITY.  (Lack of a dream)
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• 4. INSUFFICIENT EDUCATION.  (This means knowledge... not schooling)
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• 5. LACK OF SELF-DISCIPLINE. 
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• 6. ILL HEALTH. (I eat Micky D's, never excesize, and don't breathe properly)
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• 7. UNFAVORABLE ENVIRONMENTAL INFLUENCES DURING CHILDHOOD. (Birds of a feather flock together.)
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• 8. PROCRASTINATION. 
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• 9. LACK OF PERSISTENCE. (Quitters never win, and winners never quit)
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• 10.NEGATIVE PERSONALITY.
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• 11. LACK OF CONTROLLED SEXUAL URGE. (Bill Clinton)
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• 12. UNCONTROLLED DESIRE FOR “SOMETHING FOR NOTHING.” 
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• 13. LACK OF A WELL DEFINED POWER OF DECISION. 
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• 14. ONE OR MORE OF THE 6 BASIC FEARS. (Poverty, Criticism, Ill health, Jealousy, Old age, Death. Fear is paralizing.)
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• 15. WRONG SELECTION OF A MATE IN MARRIAGE.  (Your spouse WILL make or break you.)
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• 16. OVER-CAUTION. (no risk, no reward)
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• 17. WRONG SELECTION OF ASSOCIATES IN BUSINESS. 
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• 18. SUPERSTITION AND PREJUDICE.
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• 19. WRONG SELECTION OF A VOCATION. (Sometimes people open a business because they think they can make money. They should really only open a business if they are passionate about the subject.)
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• 20. LACK OF CONCENTRATION OF EFFORT. 
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• 21. THE HABIT OF INDISCRIMINATE SPENDING. 
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• 22. LACK OF ENTHUSIASM. 
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• 23. INTOLERANCE. (Closed-minded)
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• 24. INTEMPERANCE. (Drunks, drug addicts, gluttons, etc...)
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• 25. INABILITY TO COOPERATE WITH OTHERS. 
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• 26. POSSESSION OF POWER THAT WAS NOT ACQUIRED THROUGH SELF EFFORT. (Think Paris Hilton, and then contrast that to Peter Buffett.)
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• 27. INTENTIONAL DISHONESTY. 
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• 28. EGOTISM AND VANITY. 
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• 29. GUESSING INSTEAD OF THINKING. (Get the FACTS straight before acting.)
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• 30. LACK OF CAPITAL. (Very common for people not to find sufficient starting capital, but for most businesses, this does not apply)