"Krapp's Last Tape" begins with the title character musing with a banana in his mouth and pacing around, nearly slipping on the peel of said banana multiple times. It's physical humor in its purest form, and the parallels between Krapp's antics and those of circus clowns are undeniable. I assumed this to be a simple coincidence, until I read "Molloy." Again, we see a caricature of a man, an absurd being in an absurd world. Again, I found myself wondering why. With the sympathetic descriptions of Molloy's bodily idiosyncrasies (a lame leg he must prop on the handles of a bicycle to ride), it seems Beckett diverged from Chaplin in that the "little tramp" is now the "everyman." This clown struggling to get to his mother's house is now all of mankind.
This stands to reason with Beckett's ideas, as he saw the world as inherently absurd, as well as presumably everyone in it. So when we see the clown on stage or read about him on the page of Beckett's works, we laugh; there's a clown and it's funny because he's doing circus-like things. But then our laughter grows dim as we start seeing ourselves in the hapless struggle. This is part of Beckett's genius, because the contrast between the humor and the tragedy within that humor makes his point hit all the harder.
It's like that old joke (ripped shamelessly by me from Watchmen): "Man goes to doctor. Says he's depressed. Life seems harsh, and cruel. Says he feels all alone in threatening world. Doctor says: 'Treatment is simple. The great clown - Pagliacci - is in town. Go see him. That should pick you up.' Man bursts into tears. 'But doctor,' he says, 'I am Pagliacci.'"