A classic lateral-thinking puzzle: 11 eggs are in a basket and 11 people each take one egg — yet one egg remains in the basket. How?

The last person takes the egg together with the basket — so an egg is still "in the basket," now in that person's hands.

The trick:

• Vertical thinking assumes "take an egg" means remove the egg and leave the basket
• The puzzle never states that — the unstated assumption is the trap
• The last person simply picks up the basket (with the final egg inside), satisfying both "everyone took an egg" and "one egg is still in the basket"

Why it matters:

• This is the essence of lateral thinking: the solution requires rejecting an implied rule that was never actually stated
• In security, attackers win the same way — they exploit assumptions defenders never realized they were making (e.g., "no one would add a credit card just to read the last four digits")

Tip: Whenever a puzzle seems impossible, list your assumptions explicitly — the answer is usually hiding in one you took for granted.