So three guys were condemned to be guillotined: a drunk, a priest, and a professional engineer (pick your university here). As a courtesy, they were each asked in turn which way they would prefer to lie on the block.
First, the drunk: "I'd be sick if I lay on my gut, so I'll face up." Up went the blade, click, whooosh, BONK, IT JAMMED.
Following mythical tradition, the drunk was set free.
Next came the priest: "I prefer to face Heaven, regardless of my crimes." Up went the blade, click, whoosh, BONK, IT JAMMED AGAIN!
Again the tradition meant that the priest too was set free.
At last came the engineer: "A cursory statistical analysis indicates that the probability of my living obtains best in the face-up option." He lies down, facing up. Up went the blade again, but before it was released, the engineer interrupts: "AHA, I SEE YOUR PROBLEM!"