For people that I've seen do it, it's a hiding place for them. If they psychologically set themselves up for failure, then they are prepared for the "inevitable" comments about how they failed or are useless or whatnot. If they succeed though, then it will hurt worse when they are told that it doesn't matter because they're still useless and won't live up to some standard. It's a defense mechanism; better to be ready to deflect than to leave yourself vulnerable and get punched in gut.

For example, my wife was self-employed for a time. She was good at it too. She was pulling in money and developing a client base and I was cheering her on like an NFL cheerleader. She was feeling great. Then she called her mom to tell her how successful she was and her mom responded that, "Yeah, that's great. Did you hear what your sister did!?"

It crushed her because she left herself vulnerable and when she didn't get the recognition she desired, she started self-sabotaging; not making calls, not handing out business cards until it all fell down. Now when her mom doesn't care about her success, she can look at herself and feel safe because she isn't searching for that recognition anyway.