IF

A teacher once stood in class and told his students with a firm and serious tone: I am throwing a party tonight, but tomorrow you might have an exam and you might not. Those of you who show up at the party tonight will fail the exam, if it takes place and those who don't will pass, again if it takes place. Remember there might be an exam and there might just be another normal day. It's your choice.
Next morning, all students showed up in class; those who were at the party were teasing the rest about how fun the party was, and those who weren't were saying: we will see who will laugh last. Some of those who studied all night were arguing that there would certainly be an exam for there is no meaning to the dilemma otherwise. Some of those who partied all  night argued that there certainly won't be an exam for why would the teacher throw the party himself. Some were in doubt, among them were those who went to the party with a high sense of guilt and those who missed it but wished they were there. The students argued for hours, they started fighting, blood was spilled.

The teacher never showed up.

Even if paradise and hell were a sure thing, I still wouldn't give up the sinful joys of life if only as a mere act of rebellion. Why would I want to spend the rest of my eternity with such a manipulative super being?

Imagine this alternate ending: Next morning, the teacher shows up. Silence. The teacher spoke: those who attended the party may leave the room. The rest of you here is your exam: Describe last night's party.