To say a WR should catch every ball that hits them on the hands is incredibly naive. There are so many balls that, even if they hit you on the hands, or nearly impossible to catch.
Yes as a competitor and WR, you are going to say "I should catch that ball." But in reality you can't catch a 100mph (slight exaggeration, as I you tend to think I am being quite literal with everything I say) dart at 5 yards away. No can you catch a ball that is thrown so far away from you that you can only get your finger tips on the ball.
It is naive and cliche to say "Every ball that you touch you can catch". Yes I applaud and encourage the mentality, but since you and I are not on the team playing the game there is a level of common sense that needs to be applied.