See, this is happening in all areas of my life, which is why I say repairing self-confidence will help in general, not just Wing Chun.
Example: I do something that hurts my girlfriend's feelings. Well, I am an awful, hurtful, mean person. The double whammy comes when I say, "Gee, all she does is complain about me." However, the thing is she compliments me way more than she criticizes me. And it isn't REALLY criticism. I mean, if you do something that hurts someone's feelings, then they should have the right to tell you so you can apologize and do better in the future. (The only way it would really be nitpicky is if someone is oversensitive, which she is not.)
Then the part you said about avoiding failure comes into play. If the hurtful offense is bad enough, then I might think to myself, "Geez, I am an abusive A-hole of a boyfriend. Maybe I'm just not meant to have deep, meaningful relationships with anyone." And the urge to split occurs.
Or I should say OCCURRED...past tense. But I fought against it. I fought against running and being a coward, facing down WHY I act that way and doing something about it. The same can be done regarding chi sao, regarding why I didn't get a promotion at work, regarding ANYTHING.