Confirmation Bias

It is common for people to commit the confirmation bias fallacy: When they want to prove something is true, they give a case when it is definitely true, not when it is possibly false.

You say your stick is as hard as steel. You hit it against a pillow and go "Yea, yea! look how strong it is! Yea, yea!"

If I wanna prove something is strong, I'll try to break it. If it holds together, then will I know that it IS strong.

... or at least strong enough under the conditions that I tested it.