Riddle:
If boiling water is poured into a thick drinking glass as well as a very thin wine glass. Which of the two is more likely to crack?
Answer: The thick glass is more likely to crack since glass is a poor conductor of heat. In a thin glass, the heat passes more quickly from the glass into the surrounding air, causing the glass to expand equally. When hot water is poured into a thick glass, the inner surface expands, but the outer surface does not. It is this extreme stress on the glass that causes it to crack.
Riddle:
I weaken all people for hours each day. I show you strange visions while you are away. I take you by night, by day take you back, none suffer to have me, but do from my lack.
What am I?