It is sort of like asking a weight lifter how much they bench press. If a guy could bench 240 LBS, there is a good chance that he will tell you that he can press 275 or even 315. It is usually very enlightening when you find yourself in the gym doing bench presses with that same fellow. Suddenly, your companion is telling you that he hasn't warmed up properly, or didn't get enough rest, or went heavy last workout, so he is still a little fatigued.
I know, I've been on both sides of this equation.