Why do most traders think that they will become profitable?

I think a big part of the answer to this has more to do with "which people become traders" than with "what traders decide to believe", in the sense that in order to have become a "trader" in the first place, a person must - by definition - already have envisaged at least the ability to win.

So it's kind of a self-fulfilling observation, by definition, perhaps?

Kprsa and KarlKraus brought up interesting points.
So in order to wven have a chance of becoming successful at trading, one must 1) have some required qualities already, and 2) be persistent?

I once asked a somewhat successful (by the local standards) construction materials business owner :
Can you give a tip on how in your opinion one can become successful?
He gave me the following answer :
1) Find something which you truly fall in love with. Otherwise it would be nearly imposible.
2) Start building a foundation of knowledge on the subject. Than continuously build up your knowledge more and more untill you become a master of your craft.
3) Money will come towards you.

I used to view trading as an art, now I see it more of a science. But wait, art is a science in itself isnt it ?
I simply fell In love with trading, I've spent countless nights researching and learning. Though It wasn't much of a work for me, it was pleasant because I was simply learning my hobby. However I've come to the conclusion that one must master this art to the point that it becomes like science.
Painters for example do art, but to them even drawing a human silhouette is a science of its own, with clear rules (proportions).

To me it looks that the more talent one naturally possesses, the less hard work is needed. Just like everything else.
k

It's their psychological that makes trader ego buy/sell with their feeling of market that come to failure. Trade what is shown on market.

Not exactly. A person comes to Forex because in real life, he struggles to win money and he is looking for an easier way to make money from home. It sees at as his only chance to make money, buy a nice car, house, get a beautiful wife....
When he starts losing money, he can't just stop. Stop ?! No way, what about his dream ?! So he asks the question here and other los...oups...I mean other successful traders with a beautiful red square tell him you need to persist and spend more time in front of the charts...money is right around the corner...and then he keeps trying and trying and trying...
This is not bad after all because dreaming is like living...well almost...a kind of...

Honestly, most "traders" lack discipline. So, why they tell themselves they can be profitable without it is beyond me. Discipline can be learned, but not by everyone. If you have never been able to discipline yourself to something in life, then you don't stand a chance in this business or likely any other business for that matter either IMO.