A psychologist named Karl Duncker created this in 1945.
He brought the experiment subjects into a room and he said,
I give you a candle, some thumbtacks and some matches.
And he said to them,
Your job is to attach the candle to the wall so the wax doesn't drip onto the table.
Now what would you do?
Some idea like this; Light the match, melt the side of the candle, try to adhere it to the wall.
this kind of the way to try doesn't work.
And eventually after five or 10 minutes, most people figure out the solution, which you can see below.
The key is to overcome what's called functional fixeness.