He's literally made the same mistakes as he has with ALL THREE of the big DBZ villains.
He chose to spare him at a golden opportunity to finish him, just like with Frieza.
He failed to stop him from absorbing someone else's power to beef himself up and turn the tide, just like with Super Buu.
And now he's faced with an impossible choice, where the enemy is set to explode, taking Earth (and the galaxy, I guess) with him, as with Cell.
To quote TFS Piccolo:
"Which one was it Goku? Which concussion did you suffer that made you think ANY of this was a good idea!?"