@xieshuyu Answers to your Q's:
Q.What's the key to happiness? Freedom?
People mostly through all sub-parts of Freedom (which can be other things but mostly people orientated and transmitted) which could be labelled freedom or spreading more love / consideration / consent / values (non-numerical).
...More words to learn and re-teach here is wanted
http://freeschool.0id.org/love-value-my-words-list/

List all the tasks to do and carry them out one by one and repeat this process?
Yes, do that more than not.

Is there any fulfilment in that?
Yes. There is a chance that if we chain things suddenly tomorrow things can be much better from all the patchwork we do, if we can link them or use them as fuel. Like a chain of love / loving thing rather than working for wrong people.

The other comments I will mentioned in passing:

> temporary success doesn't mean nothing to me anymore
Good you are realising where to put your effort and what will hold better as container for efforts and your intentions (money quickly wastes it away and you have to throw more money there, it's by nature of banks and %'s wasteful / temporary). Personal fulfilment and contact with others 100% different realm... not numbers

> I begin doubting whether I did was anything meaning or even worth celebrating

Because we don't know many things YOU and WE have to create our own reasoning and celebrate and dance during that both to pass the time but at the same time be good caretaker or planet and people and let the rest do it's thing... not over manage.

More questions welcome.