Some people think that pugs are stupid because some pugs are hard to train. It's not that they're stupid, it's just that they are extremely stubborn. Maybe they know what you're trying to tell them but they don't want to do it. Maybe they just don't care. It's a trait that can be incredibly frustrating, hilarious, and entertaining.
Sunny is the worst - she's the most stubborn dog I've ever met! If we're out on a walk and she doesn't want to move she will just plop her big ol butt down and refuse to budge. Sometimes, not even food is enough to convince her to do something. Rosy on the other hand is a people pleaser and a food monster so it's pretty easy to convince her to do anything.