I just thought it was such piss poor judgement on his part that eventually got him killed. I know he was trying to expose the truth of the crime, but he let his guard down big time... and around The Mountain. Who does that in Westeros? :P

Bronn pretty much had the right idea. "Maybe I could take him. Dance around until he's so tired of hacking at me he drops his sword, get him off his feet somehow... but one misstep, and I'm dead."