Death Note
Light is shown to be a pretty intelligent kid at the start of the series but the heat he starts catching was the result of him doing some stupid shyt. Sometimes I wonder if dude wanted to get caught because some of his moves I wouldn't even have considered.
Light gains the power to kill folk at any range without being present and leaving no kind of evidence just by getting their face and full name in mind through supernatural means, he's also cautious enough not to kill people he knows, and creates a fail safe to destroy this power source in case someone gets too close.
His biggest mistake:
He starts killing criminals and stays under the radar for a good while until a detective suddenly comes on TV and starts spitting ether, calling him out and talking about how he'll catch
Kira. So Light drops that nikka on live television despite the fact that there was no real way that detective would ever get close to his identity.
WHY??? Goddamn... All he had to do was ignore the broadcast and keep on killing. Turns out the broadcast was a trap which gave the real detective some big bread crumbs like Kira's locale, the clue it's most likely a student doing the killings, and certain limitations to his killing power. Fail.