I think I can influence my emotions, to some degree, by controlling what I think about and how I act. It's a lot of effort, though. Sometimes when I've been depressed I've had this cycle of "I should do x to cheer myself up" followed by "no, I deserve to be miserable" and so I just sit and stew instead. O_O

But even when positive thinking works for me, it's never been as easy as "just decide that I like it". It's the sort of mental effort that's hardest to make when I need it most. And at its worst, it just makes me feel more awful for not being able to do it better. It should be easy! They're my emotions, right? Why can't I tell them what to feel? Dammit, where's my owner's manual? >:)