Teen Wolf, Season 5

[Scott and Melissa are in the morgue, where they're staring at Lucas' dead body]

Scott:
I should've done better. I... I... I should've known that this was going to happen. I should've been able to stop it.

Melissa:
You know, your grandfather used to have a saying about the word "should." You know what you're doing when you say "should" too often? You're should-ing all over yourself!

[Scott laughs weakly, but still seems upset]

Melissa:
I know that I can't be the mom that says "I don't want you to do anything about this," 'cause you're always going to be involved. Because not only do you have the power to do something, you care enough to do it. So, all you really need to ask yourself is-- "What am I going to do?"

Scott:
[determinedly] I'm going to find out who did this... and I'm going to stop them.