First, it's easier to keep dangerous emotions out than to control them once they're in. It's easier to refuse them entry than to manage them after you've let them in. Once they've taken over your mind, they become stronger than the rightful ruler. They won't allow themselves to be weakened or reduced. Second, Reason herself — the one who should be in charge — is only strong when she stays separate from these emotions. If she mixes with them and gets contaminated, she can no longer restrain the very passions she once could have cleared away. Once your mind gets stirred up and shaken, it goes wherever the emotions drag it.
In the first place, it is easier to banish dangerous passions than to rule them; it is easier not to admit them than to keep them in order when admitted; for when they have established themselves in possession of the mind they are more powerful than the lawful ruler, and will in no wise permit themselves to be weakened or abridged. In the next place, Reason herself, who holds the reins, is only strong while she remains apart from the passions; if she mixes and befouls herself with them she becomes no longer able to restrain those whom she might once have cleared out of her path; for the mind, when once excited and shaken up, goes whither the passions drive it.