A play with a negative expected value is a mistake in poker. There are two types of mistakes, small and big. Let’s focus on the big mistake for this one. A big mistake is something with a big negative expected value.
To analyze how big your mistake is, you must size up the pot because the size of the pot affects the expected value of a player’s decisions at the table. If the expected value is bigger than the amount of bet then you should go ahead and make the call.