Commonly accepted notions don't hold much weight among Psychologists.. In our first class we spent the entire three hours being shown that the majority of even decently educated people accept pop psychology as real psychology because the explanations become so common that people just stop questioning it.
Projection is actually a very specified coping/defensive mechanism that only certain personality types adopt. It depends on social factors, how parents argued, self confidence, all kinds of stuff.
When your average intelligent adult strongly dislikes something, it's a less than 25% chance that they're projecting, and over a 50% chance that they're associating the supposedly innocent target of aggression with some other external image or moment that creates those same feelings.
Not logical, but it's the actual most common source of random anger with very distinctive ideas or images that haven't caused harm to the person feeling it.
I wish I wasn't such a compulsive nerd at times lol