First off, success is different for different people. However the grass is greener on the other side. Now that I have put penned down cliche bullshit let me explain why.
Failure is the occurrence where the goal you set out to achieve could not be achieved. This is often due to changing circumstances more than laziness (at least from observations and readings). We all expect a linear world but we live in chaos and try to make sense of it through linear models.