A lot of importance is placed on statistics in football nowadays—chances created, key passes, tackles per game and so on are good mathematical markers to judge a player on.
You cannot put a statistical value on the word tenacity, but if you could, you'd give Jack Wilshere the highest possible mark.
Wilshere had a statistically unimpressive game in Arsenal's 2-0 defeat to Manchester City, yet he performed superbly. He may have scored the only goal against Swansea, but he was having his best game since he played Barcelona even before that, through sheer effort and commitment to the cause.
Arsene Wenger can't trust all of his players to introduce this element to their games, and it might well be a product of his graduation from the Arsenal academy.
If Aaron Ramsey showed the same mental strength his colleague does, he'd have every chance of becoming the star Wilshere is certain to be.