GSP has lost twice, once by armbar to the legendary WW great Matt Hughes, and once to Matt Serra.
One TKO loss in 26 professional fights, with so many happening at the highest level, does not equate to having a "weak chin", or "being a pussy", or whatever other nonsense that GSP haters like to spew.
GSP has been criticized for not finishing and I can understand that. It even frustrated me sometimes, when he would be so dominant but step it up to go for the finish, but I could appreciate him for what he did...which was make his opponents look like they didn't belong in the cage with him.