I have a theory. The tougher someone says they are, the less tough they are in reality. For instance, if you ever met a guy in bar who says he can take out the whole bar with one hand tied behind his back, you better believe he would be the first person to run and hide if a fight were to ever breakout.
Similarly, if anyone ever tells you about all the fights they have been, to find the actual number you should subtract by X, where X is equal to whatever number they just said.
But if someone is quiet and just keeps to himself, that might just be the person you should expect the unexpected from.
Take me for instance, I would never tell you I once killed 30 men with nothing but my wit and my bow-staff, and because I would never tell you, you know it must be true. Right?