Mistake(s): Gohan has not made a huge amount of mistakes, but nobody is perfect. During the Cell Games, Gohan was holding in a lot of power and basically toying around with Cell even though he honestly could have killed him from the begginning. By not killing Cell right away, Cell started to grow like a balloon and it forced Goku to transport to King Kai's planet where he died. Another mistake would probably be trying to take on Buu when he first saw him because he just got knocked out badly.