Agree. Premature ejaculation is incredibly frustrating. Most people who don't suffer from it think, its like a 20 minutes fuck that only goes for 3 minutes, a start, a middle with a crescendo, and a climax. For me at least, its nothing like that. Unless i'm masturbating, I have no clue, hint or sense if i'm about to cum until its too late.
So, I can't fuck, stop wait until that feeling subsides and then start again. I can fuck, think i'm at least another minute away, and on the next thrust, start cumming without warning. Its still feels ok, but a lot of the time its like a ruined orgasm while you hurridly reach for your cock and try to wank it the last squirt or two to a somewhat pleasurable outcome.
Or as you say, you may feel in control, then a finger to your asshole, or your nipple sucked and you'll cum uncontrollably. Its really frustrating, because you never, ever achieve the powerful orgasm your hoping for, whereas as with your own hand you have a lot more control over when to cum.
Its definitely mental, we use condoms a 99% of the time for this reason, sometimes cock sleeves, but even if I feel next to nothing, a certain move, word whispered will have me cum without me wanting to.