The winning blow was on the board and the clock was not the problem — you played safe instead of decisive.
There was a forcing shot on the board — a check, a capture or a direct threat that wins material or mates by force — and a quiet move let it slip past. The cause isn’t talent, it’s a missing routine: before every move, look at every check and every capture first, for both sides. Forcing moves before quiet ones, always. Train that scan and these points stop vanishing.
The good news: it is a pattern, not bad luck — and patterns can be trained. Step one is measuring yours: how often it appears in your real games and how many rating points it drains. Then the daily repair: 5 minutes on your own positions, not invented puzzles.