Why do we believe people when they say they work hard or used to work hard? Most successful people I've observed at close quarters box clever and definitely ne

Why do we believe people when they say they work hard or used to work hard? Most successful people I've observed at close quarters box clever and definitely never fully switch off with respect to their interests. But work hard as in slogging on something where there is no proportional reward? Never seen that. Of course they all say they work so hard, or that they once in the mists of time worked very hard. But what evidence is there? Usually none.