It's not fear of the past. It's learning from the past.

[Neutral or not, Ezra still feels a flicker of defensiveness at Qui-Gon's words.]

You have to think about what could happen if you don't want stuff that's happened before to happen again.

[Despite the argument, though, he's not feeling truly argumentative. Maybe it's because of the vague depression that surfaced with his regrets, or maybe it's because part of Qui-Gon's admonishment does strike a chord with him. He really can't make his goals for the future a reality if he doesn't actually do something in the present. So when he takes his next breath and slowly lets it back out, he really is trying to let his feelings go out with it.]

Being a Jedi is hard.