When the going gets tough, it's even more important to take care of yourself, not less. It's easy to justify letting something go, like going to the gym or making a somewhat healthy meal. It's even easier to justify letting yourself go emotionally, like not taking a sick hour or pushing yourself to the point of stress at work.
If I prepare myself for tough stuff that's going to happen by putting me first, I'll be able to be more there for myself and other people.
this article contains a gem that summarizes this nicely: "The moment to take a breather is at the exact moment you feel like you couldn’t possibly do that."