I think people may misunderstand what he is saying.
What he is getting at, is that people will ALWAYS complain about the bad things, no matter how small these bad things are. However, the good things will usually go unnoticed.
IE, if you ask for a plain cheeseburger and get pickles and onions with it, you are going to go up and yell. However, if you order a piece of cake and it ends up being the best thing you've ever eaten, you likely won't go up and tell the cashier about it.