Once a wise and graceful king, Cymbeline seems to be a kind-hearted guy led astray by an evil Queen. Let's just say that Cymbeline may be king, but he's definitely not the king of good judgment. We learn, for example, that he also banished Belarius twenty years ago even though he was loyal. So is this one dude who's easily fooled? Is the Queen just that good at manipulating him? The play lets us be the judge.
Cymbeline tells us that his wife was beautiful and flattered him, as if it's not really his fault he got himself in a pickle. After all, he says, "Who is't can read a woman?" (5.5.58). Translation: she was hot, so I believed everything she said. Well, what can we say? Cymbeline is neither the first nor the last politician to let himself go over a female.
(Guess it's a good thing Imogen found the Queen out before she could poison the king, though, right?)
Cymbeline does have one thing going for him: he seems to be truly concerned about the harm he might have caused with his foolishness. "Heaven mend all!" he cries out (5.5.80) in the final scene, once he's figured out just how much he was duped. It can't be fun to have your dirty laundry aired in public—especially in front of all those British and Roman soldiers you've brought to war for no good reason.
It's not necessarily that Cymbeline is a weak guy. His problem seems to be more that he's overgenerous, and that makes him easy to manipulate. He's ready to forgive and forget pretty much anything. You've waged war on his country? He'll forgive you. You've married him for power? He'll forgive you. You've kidnapped his sons? He'll forgive you.
Now, that kind of generosity can be a sign of strength, but it can also get out of control if you don't have good judgment to back it up. And we hate to say it, but good judgment isn't really a skill that Cymbeline should be putting down on his resume. He's pretty much the only person who doesn't realize something is up with the Queen, and that's because he doesn't understand that he could have the hots for somebody who isn't good for him. How old is this guy—15?
Let's look at an example. When Cymbeline hears Belarius's account of what happened to his sons, he declares "the service that you have three done is more unlike than this thou tell'st" (5.5.428-429). Let's get this straight: when his daughter marries someone in secret, he banishes her husband and locks her away. When his wife says she doesn't want to pay a silly old fine to Lucius, he starts a war with all-powerful Rome.
But when someone kidnaps his sons and brings them back twenty years later, he says, well, let's call it even. We're not really sure why Cymbeline forgives Belarius at the end of the play: maybe he's trying to turn over a new leaf and go back to being an easygoing guy instead of the malicious angry man his wife led him to be. Or maybe he really is so overjoyed at seeing his boys again that nothing can ruin the best day of his life.
Whatever it is, Cymbeline's forgiving mood at the end of the play sets the tone for a happy ending. We like to think now that everything's hit the fan and Cymbeline has seen how foolish he had been, he's got the good judgment to know which things should be punished and which things shouldn't. It's Cymbeline's own fault that Belarius was banished, so by accepting Belarius back into the fold, it's sort of like Cymbeline's acknowledging his former toolhood and turning over a new leaf.