This is super important. Non-founders often will not get it, in my experience. If you haven't started a company, you often will not have experienced the intense ups and downs, and just how fucked everything can be, even when you pour your life and soul into it, and that there really can be a light on the other side of the tunnel.
One brief tip: it is OK to give up your startup - don't feel that you can't.
If you're in a dark place, do take up the kind offers that people are making in this thread. (I'm paul@circleci.com if you want to chat, and I've publicly fucked up one startup, so I understand.)