Interesting question to ponder isn't it?
What would be the reason for you to achieve or do something?
Academically, one would mention god as their main factor. It can be true, it can also be hypocritical. Different people have different reasons i believe.
One of the common factor would be vengeance. Seriously. The more hurt one gets, the more one would one to get back.
How many times you have heard: ..
"I will prove it to him that Im not as fat as he thinks.." or
"Siap kau. Nanti tengoklah aku boleh berjaya! Aku baling-baling duit kat muka dia.. "
Systems of justice… for example, can be regarded as the successful transformation of a deep-seated urge for revenge – euphemized as retribution – which keeps the urge within acceptable boundaries
Frans De Waal,Good Natured, p. 194
In a way, it is quite sad if this was the main reason to achieve a feat. The achievement should be for oneself to be happy with and not for others. However I am sure many of us had fallen into the trap of doing something for somebody else and not for yourselves.
I do blame parents (in general) at times because this would be the first motivation factor for some people to complete something for. I've known doctors who went through medical school for their parents and when they have graduated, they endevoured into something totally opposite. Take Chef Wan for example, he was a certified accountant but he did not have any life satisfaction until he pursued his culinary dream.
I have had my fair share of getting even. It was a strong motivating factor as it kept me going. Betul-betul macam dark side of the force.. haha However along the way i have discovered the true meaning of achievement. It is totally for your own fulfillment. Only then you will be happy with your life. Whatever you achieve is for you and if there is only one person that you want to prove it to, it should be to yourself. Never for somebody else.
It was not easy to get out from vengeance. The sweet smell of revenge has always been the motivation factor. However, I've learnt to let it go and Subhanallah, I've never felt better.
So bros, let it go!
p/s haha not the Disney version ok!