Happiness is

My hard work doesn’t pay off

Let’s say you could achieve 100% of your goal based on your abilities, but it would still be a success if you only achieved 70%. The problem is that most of us expect to achieve not 100% or the more sensible 70%, but 120%. Naturally, holding this unrealistic expectation
leads to disappointment. 

 If you feel defeated because you failed, it’s because you expected more than your efforts could earn you.  Examine why you failed and then make an effort to improve. That process would be a big success in and of itself.