I think that to get fit and lose weight need not be hard. I mean there are many days when I come under my calorie budget and I have had an hours exercise and never felt like I was enduring any great hardship.
But it is not always like that. I think what this tells me is that the urge to eat something I don't really need or the reluctance I might feel to exercise are really all in my mind. I'm not really hungry, rather I'm bored or upset or depressed or worried or stressed or ...
So to the subject of this post, determination. If your weight loss or fitness plan is making your life hell then perhaps you are doing it wrong, so look at the practicalities (e.g. You need a calorie deficit but you can still eat foods you enjoy) . Then when you have found a way to get it right on your good days show determination to ensure that everyday is a good day. You do need to be determined to reach your goal but to do that you need to be determined to solve problems that get in your way rather than to starve yourself or slog your guts out. So if boredom drives you to food find distraction, if depression does then get help, if temptations do then avoid them.
Keep plugging away but remember it need not be hell. And that persistence is more important than perfection!