when we give up in our mind, period.
Failure is not when we experience it.
Failure is not when we are not able to get what we desire.
Failure is not when we are not able to achieve our goals.
It is when we stop trying. It is when we are defeated in our minds and give up. Most of the times, the eventual success was an inch away (and I agree it is hard to realize that) but we stopped trying. Success, most of the times, is traveling the journey itself, rather than the end goal – that just proves to be the icing on the cake. The things, knowledge, wisdom and habits you gain while trying is your success which will shape your future.