These are the struggles that are forever, that are life-changing and cannot be changed.
If that relationship you're in is toxic, it really can't bring out the best in you and you should probably free yourself from it.
If that relationship you were in has been over for some time but you're still clinging on to memories or hope of it rekindling when it isn't going to happen, let go because you can't move on when your head is still holding on to the past.
If that job isn't satisfying or you feel like you aren't getting enough out of it anymore, change it.
If you're in constant battle with your own motivation to get up and go for that walk or run in a bid to better your fitness, then you have to want it enough. If you don't and you'd prefer to lounge on the couch, eat those goodies or sleep as much as you can - that's not a problem, just don't complain about it.
Most of the time, if you're unhappy in a situation, you can change it. If that is the sort of problem you have, you should be grateful because there are others who are dealing with struggles that cannot be undone.
Let's remember that as we start 2018 - don't face problems you don't have to when you can make the decision to be happy!