The smartest MCU villains are often outsmarted in the most mundane of ways. As it turns out, when a villain spends all their time dreaming of grand schemes of intergalactic domination, they can forget about the little things in life. And, then, heroes can exploit those little things to utterly destroy the villains and end their reigns of terror. (Luckily for these villains, just because they have been utterly destroyed doesn't mean they can't return to the land of the living.)
Not even the most intelligent MCU villain dreaming of the most evil MCU plans can stand a chance against these clever heroes. Whether it is a sleight-of-hand technique that brings down the great Titan or a movie reference that ruins the day of an alien conqueror, it apparently doesn't take too much thinking to take down these genius villains.