According to the text below, one prime difference between a tzaddik and a regular person is the tzaddik believes Hashem gives him the koach to fix himself; he knows he doesn't have it on is own.
But that's okay in the tzaddik's eyes because HASHEM can grant him success.
A regular person relies on himself, on his abilities & strengths, which brings despair after the first couple of falls.
"I can't do it," he says. "So there is no hope. I simply don't have what it takes. It's not who I am."
But the one who eventually becomes a tzaddik says, "I can't do it...but HASHEM can! I don't have what it takes...but HASHEM does! It's not who I am right now...but HASHEM can change that!"
Here are the words of Rav Itamar Schwartz (boldface my addition):
From where does a tzaddik have the power to fall and get up and fall and get up again?
A regular person, if he falls once or twice, says to himself, “I fell and tried to get up but couldn’t do it, so the next time I will fall, I will not be able to get up either.”
If he fell twice and couldn’t get up, on the third time he will feel that now he has a chazakah, and for sure will not be able to get up.
But a tzaddik believes that Hashem gives him koach to fix himself.
With the power that Hashem gives, one can succeed in anything.
If it was my own power, it is limited and I can’t succeed, but if I receive every day a new power, the question is Who gave me the power?
On this Chazal say:
“Hashem li b’ozrai — Hashem is my helper.”
Therefore even if in the past you failed, a person knows that Hashem helps him.
Therefore there is never a place of despair because he knows that Hashem will help him even if he fell many times.