Self taught programmer here, criticism is something I think is harder for self taught people. I think it stems from never having an authority over you when you initially learned, and that sort of becomes enshrined as part of your identity. If your not reviewing someones code formally, just ask questions that could lead them to what your trying to suggest. Pretty commonly used method but just having them logically work it out sort of quails the knee jerk reaction to criticism.

Also maybe a lot of people are self conscious about no formal education as well? That wasn't an issue for me but I imagine it is for some.

TL;DR: The transition from learning the hard way always, to allowing someone to try to prevent it is tough.