Understand failure to understand success

All of us always want to succeed in life; it is quite a natural desire. When the desire is natural the fulfillment should also be natural. Yet we observe failures happening in our life and in lives of others. Why is it so?

In order to understand this we must understand that nature is always perfect. The sun never fails to rise, earth never fails to rotate, and birds never fail to fly. Then why human beings do not always succeed in their endeavors?

What exactly causes human failure and what needs to be done to correct this?