It is said that a story can only be as good as its antagonist. In this regard, the Marvel Cinematic Universe is all over the place, with the likes of Thanos, Killmonger, Loki, and Wenwu being balanced out by Dreykov, Malekith, Ivan Vanko, and Ronan the Accuser.
Quite understandably in a shared universe this big, the heroes will always get more time for development across multiple appearances, while for the most part, the bad guys will suffer for it. However, regardless of whether they are good villains or bad villains, there is usually a point when they say or do something that just isn't that smart.
No matter how much of a problem a villain can seem, whether they are threatening a business empire or the entire multiverse, there are times they will make things just a little bit easier for the heroes with a stupid decision or two.
Refusing to kill an enemy out of arrogance or even principle, revealing too much of their evil scheme, and putting too much faith and trust in someone who didn’t deserve it have all led to a villain’s defeat and often demise far sooner than it ever would have come otherwise.
10. Justin Hammer Trusted Ivan Vanko
Justin Hammer wanted to be Tony Stark. There are no two ways about that, he wanted everything that Tony had, from the money to the fame to the women. He had the attitude and the self-confidence (though his was completely unearned), but he lacked just about everything else.
With the government at odds with Stark over the Iron Man “weapon”, Hammer saw an opportunity for his company to slither in and mop up the contracts Stark was losing. This included him kitting out the entirety of the USA’s armed forces.
This was a strong plan, utilising his enemy’s weakness, however for his plan to work he had to put a lot of faith and trust into a man that neither deserved it nor earned it. In Ivan Vanko, Hammer found an ally that was never interested in mutual gains, he just wanted revenge on Stark in a different way.
He forced Hammer to waste his money, he destroyed his presentation at the Stark Expo and any chance he had of getting into the Pentagon, and the crushing irony is that had Hammer just done nothing and bided his time rather than trust Vanko, Stark likely would have imploded all on his own and left Hammer Industries to pick up the pieces.