Esther Inglis-Arkell at io9 posted an article called An experiment shows how people deliberately sabotage themselves, in which she explains that self-sabotage is not a subconscious impulse, but a clear, conscious decision:
Two researchers, Edward Jones and Steven Berglas, asked students to take a test. They pretended to score the test and happily told the students that they'd got ten a perfect score. This had to have come as good - and somewhat surprising - news to the students, who were then asked to take another test.
Before they took this second test, they were asked to take their choice of two different drugs. Both were perfectly legal, the researchers assured the students. One was designed to improve academic performance. The other was designed to lower it. Guess which ones the students overwhelmingly chose.
She writes about being "[S]o anxious to impress someone that we don't want to say anything wrong - and so we don't say anything at all, which is hardly impressive," which is a super-familiar sentiment to me. I remember in particular one time, I think in 2009, when I met Neil Gaiman, and I deliberately tried as hard as I could not to make any sort of impression, because I was terrified that he'd remember me a decade later and think I was an ass.
Self-sabotage can be a conscious experience. I don't want to say it always is, but I've never experienced it being a weird, inexplicable action that I could only make sense of far, far later. It's more like a horrible sense of dissonance between what I want and what I know my brain is about to do. Like that word vomit scene in Mean Girls. It's something I talk to my therapist about.