A Classic Example Of Functional Fixedness

If you have two candles, numerous thumbtacks, and a box of matches, try to figure out how to mount the candles to the wall.
Answer: Using the matches, melt the bottom part of each candle, then use the hot wax to stick the candle to the matchbox. Then use the thumbtacks to attach the box to the wall.

Due to functional fixedness, many people might try to use the thumbtacks directly to fix the candles to the wall. They may consider it as the only way to use the thumbtacks.