What about when there is no endpoint, though? Example the first - children! I am sure that there are some people out there who don't know what it's like to have that child who keeps you up at night (I'm not talking about crying, teething babies. They have an endpoint!). The kid whose behavior is a mystery to you or whose illness is as yet undiagnosed. You go to bed wondering how you can keep going. You just can't get through to this kid. You can't convey to them that they are making their own hell and that they alone hold the key to their own happiness. Their mind is a mystery. It wears on you. At times you wonder if you can do it all again the next day, holding your breath and wondering what the mood is going to be, just waiting for that shoe to drop. But you have to keep trying. And some kids don't just magically stop being worrisome when they grow up, either. I know that's a huge shock to parents of adult children! You keep trying, though. You have to.
Example the second - marriage. Absent physical abuse (I hesitate to say emotional abuse because I think that word is vastly overused and the definition is a very personal one), you keep trying. Until the ring is on the finger, you don't owe a person your undying effort. You owe it to yourself to make sure that you're making the right decision. Because once that ring is on the finger, you keep trying until. Marriage isn't a sprint and it isn't a marathon. It's a slog. A lifelong slog. A lot of it is uphill, and the really hard part to swallow is that sometimes the downhill runs don't come in proportion to the uphills. My friend's mother told her that a marriage is like two horses pulling a cart. Both have to be pulling in the same direction and at the same speed. Otherwise, it all goes to hell (well, that last part is my own interpretation). If one pulls in the wrong direction or at the wrong speed, it's no bueno. That makes perfect sense to me. I'm a huge fan of marriage, don't get me wrong, but it's not easy. And you keep trying until.
For most other things in life, though, look to the endpoints! If you have to get through something hard, realize that you won't be doing it forever. And find something to treat yourself with at the end!