Before the incident Phineas Gage was a level headed person, because he was so composed and well balanced, he was the construction foreman. Basically he was in charge of everyone building the railroad.
But one unfortunate day, the tamping iron he was using to pack in explosives exploded up and ran through his head. It went up his left cheek, through his frontal lobe, and out through his skull. He was very lucky he survived, but he wasn't the same.
He started using extreme profanity and being borderline rude. He drove his friends and close relatives away. It would seem like he wasn't thinking through his actions, because his brain was not able to do so. He was able to do everything else like read, write, and count. The tale of Phineas Gale was the luckiest, unlucky story of all time.