changing vs. fighting

The challenges are a daily part of our lives. The problems show up and disappear. Sometimes they get settled themselves and sometimes we need to work hard to solve them. However, sometimes they are inseparable parts of our lives for a longer period. Sometimes they keep staying in our lives and no signs of them leaving us – problems inside the family, with a job or in a relationship. But what do we do then? Do we fight them? Do we try to improve the situation? Do we try to change the others? Do we try to change ourselves? Are we change-driven or are we resistant? I admire those people who embrace change and try to work things out themselves. They are not afraid of doing risky steps in order to achieve things and ameliorate their lives. I think that sooner or later they always succeed and get what they want. But there are different ways of implementing a change. We can fight strong to change something into a better thing or we can simply dispose of it from our lives. Both ways are surely better than doing nothing but which one of them is better when you compare them between themselves?

To make it clearer I will give you an example:
You are in a relationship - it is going very bad but there are some good aspects and days too.
You have a job that you do not necessarily like but has a lot of positive sides too.

How do you know when you should keep fighting for your relationship and struggle to start liking your job and when you should just give up your job or break up with your partner? When is the moment that there is no point in fighting and the only way you can win is by giving up? How can you see the boundary between the two? Is there any way you actually can know it?

I know it is good to change things in your life by removing them when you are not comfortable with them. But don't we go too far when disposing of them instead of trying to fight and change them for better? Isn't it like continuous running away instead of actually facing and challenging yourselves and the things we want to amend?

When should we stop struggling for things, get them over with and go for the new opportunities? Or when shouldn't we give them up but fight for them?