What is the purpose of life?!

Yesterday, I saw a video of John Green where he quotes:
“ It’s like you are in forest
You come across a fire
You keep that fire going to survive
If it goes off you build a new fire
After a while if it goes off
You build another one
Likewise purpose need not be one thing
It can change with time”
I always used to wonder how can a person decide on one thing to be there ultimate thing for whole life. We live for 100 years, how can a person just keep on painting for more than 50% of his life and be happy.
Don’t that person think that some other thing like scuba diving, being a doctor, standup comedian or lawyer would not giving him more happiness in comparison to that one thing.
After which I realised that the whole game is of perspective. If we look at standup comedian being a person who will make people laugh, then we won’t connect to it at that level. However, if we see as a person who will make his audience forget every other things going in their life and make him laugh, then we will able to connect a person who wants to become a standup comedian.
