There is something really interesting, and I fell truthful from Irsay's comments.
Paraphrasing here. He states that players play the game, and they are only capable of playing their game.
This to me is so important for determining a player's value to your team. It is incumbent on all talent evaluators to really understand the game and the tendencies the players have.
When the chips are down they are going to play the game they have. Some players are built for the moment and relish the challenge and the spotlight and perform to it.
Others say a good game, state they want the spotlight, but snuff out when the magnifying glass is focused on them.
You have to figure out each players game, and determine if they are a fit with their natural tendencies for your team.
A great example is Charles Haley. He wasn't just insane. He tended to waffle on the borderline criminal side, but when the games were on the line he was all about winning, fighting and living up to the moment. He was such a great signing for us back in the day.
Take another guy. Roy Williams the WR. That was a poor fit, and he couldn't step up into the #1 role for a marque team after leaving the hapless Lions.