Well, that's really a risk, and not necessarily a bad thing. That's trying to outsmart your opponent, and sometimes it just doesn't work out. Sometimes the CTs straight up rush towards you to deny the plant rather than play the 1v1 afterplant, and seeing as the clock is running low, the only real option is to plant. Also the CTs have FULL knowledge of your position, so the duel is 50/50, whereas if you let him get a decent afterplant position by waiting, your odds of winning will most likely become worse. So faking it at that point could be a smart move, if you, obviously, don't do it often and make a habit out of it.