In movies we see the protagonist character fight but sometimes our hero can't... he falls down every time... but never loses hope.. and tries to stand up again...
In one word what it's called?
Resilient able to withstand or recover quickly from difficult conditions
At the heart of resilience is a belief in oneself—yet also a belief in something larger than oneself.
Resilient people do not let adversity define them. They find resilience by moving towards a goal beyond themselves, transcending pain and grief by perceiving bad times as a temporary state of affairs source
Perhaps you could use one of these words? I found them with a Google search of define determined, because "determined" was the first word that came to mind.
determined, resolute, purposeful, purposive, adamant, single-minded, unswerving, unwavering, undaunted, intent, insistent, steadfast, staunch, stalwart, persevering, persistent, indefatigable, tenacious, strong-minded, strong-willed, unshakable, steely, four-square, dedicated, committed, stubborn, dogged, obstinate, inflexible, intransigent, unyielding, immovable, rock-ribbed
I bolded the ones that I think fit this description particularly well.
Depending on the kind of point you are trying to make, you could call such a person indomitable to emphasize that nothing will bring them down.
You could use indefatigable to say that they never tire and always keep trying. The already mentioned relentless and persevering also emphasize the same aspect and would be more likely to be used here.
A term often used to describe such people is fighter, as in don't worry, she's a fighter, she'll never give up.
Finally, you could also use words like naive or (hopeless) romantic if you wanted to criticize this person for not knowing when to give up.
re·bound v. re·bound·ed, re·bound·ing, re·bounds
1. To spring or bounce back after hitting or colliding with something.
2. To recover, as from depression or disappointment.
3. To reecho; resound.
4. Basketball To retrieve and gain possession of the ball as it bounces off the backboard or rim after an unsuccessful shot.
A rebound as a noun is also an object or entity that you acquire as a means of rebounding, for example
Well, to those who catch the reference, there's:
I realize it's not one word, but sometimes a short phrase will suffice.
(from Monty Python and the Holy Grail)
Perseverance n. def: steady persistence in a course of action, a purpose, a state, etc., especially in spite of difficulties, obstacles, or discouragement.
Also, this is not a copy of any answer posted because people have only used persevere so far, but I feel perseverance works better given the context of the question.