Witnessing the extent of Klein's naiveté, Kyoji shook his head and left the training room. He left the young man to the mercy of the mohawk duo, who were undoubtedly badgering him to test even more dangerous applications of his talent.
Klein had been far too reckless in revealing his full ability. It had glaring flaws that could easily be exploited, potentially putting his life at risk.
What if he encountered an enemy who knew about the time limit? They could easily initiate contact, trigger a lie-based effect, for instance paralyzes him for thirty seconds.
Thirty seconds is a long time to be helpless - plenty of time for them to do some serious damage.
He should have stuck to revealing only the lie detection aspect for now, keeping the manifestation part a closely guarded secret. At least until he learned to control it better, to choose which lies became reality.