How come some people like seeing loyal characters screw up/happy characters get angry?

When I watched Phineas and Ferb,
Phineas was always happy and optimistic but one time he showed his angry side and yelled at Candace his sister, some people say they liked it. Someone said, “It’s nice to see him not always happy for once. It’s very annoying.”
Also on a show when the loyal friend who would always give advice about whatever they call you out for doing stupid things, that friend got into peer pressure and stole something. I was shocked. She’s usually the good friend. Also convinced her friend to do it so they won’t be known as babies.
Some people say, “Honesty it nice to see her do something wrong for a change. She always seems perfect. Nobody is THAT perfect.”
“Even the most loyal friend does stupid shit and I’m glad they did it. It’s nice to see her be the screw up for once.” “Shows that even good people screw up. I’m glad they made her be the bad guy.”
Why do people like seeing that? It’s that they WANT the loyal/happy characters go down. That’s harsh.