Why do we do what we do?

i am doing my revision just do, and a sentence come across my mind. "Why do we do what we do?" Seriously in doubt...who ever question himself, what he is doing and why he needs to do this.

Honestly, i don't as my life path seems to be so normal and nobody will question me, except myself. If i am to ask myself this question, the answer is definitely...i dunno.

Guess it's time to sort out the answer for this question...