The simple answer to the very complex question is; we are afraid of success. We fall because we are scared of heights.
Lets look at this equation from a physical sense. Imagine that you are a mountain climber who is afraid of heights. The moment you reach 10-15 feet, you fall. You pick yourself up and start climbing. Again and again. People around you wonder aloud. "What a brave person (s)he is". And having reached the first cliff at 20 feet, when you raise up your arm and say I am satisfied, people will cheer you on. If you had reached the height on your first try and had called it quits, you would be treated as a coward, One who settled too soon. But now you are the hero. Who conquered it all and would not say quit.
We all knowingly or unknowingly employ this routine at many junctures in life. Some people are unaware of this strategy at work even when they employ it. Some use it as the last resort and some open with it. While there is an ocean of difference between the first and the last, the technique is universal.
The beauty of our world is that it glorifies failures and turnarounds much more than actual successes. Everyday thousands of soldiers stand guard over many national frontiers and guard it with such perfection that no infiltrator in the right mind would choose that passage for incursion. But when mismanagement and logistical gaps lay an easy way for such attacks, those soldiers laying down their lives are heralded as national heroes. I am not saying that their actions lacked bravery, I am just pointing out the thousand others who have equal if not more patriotism and live and die unrecognised and am asking; "what about them? Don't they deserve the same, if not more?"
The concept of failure is a strange one. We have always believed that failure is a bad thing and success is the best option. But as we go deep success in the first try garners less applaud than a string of failures followed by success.
Some things are funny that way. These things are as obvious as the elephant in the room, but someone has to switch on the light for you to see the gentle beast.