Failure to surprise

I sometimes write fiction, and that fiction has problems. One problem is that I find my protagonists boring. Why? What could I do to make them more interesting?

I think one reason I find them boring is that in the way that I write them, they never (get a chance to) surprise me. Frequently they don't act like they want anything, so there is nothing to be surprised about. A few do act like they want something, but then what follows is not surprising. They either get it or they don't. They may face obstacles, but overcoming those obstacles doesn't require the character to reveal anything about themselves. I may make them fail, but not enough. I forget to make things harder for them. (Pretty much the exact mistake described in that post: "there is the staple remover in the corner!")

Generally, I probably need to try and practice the ideas from that post. Also that other one. Maybe in editing before practicing in drafting.