I'm thinking about doing another 50K ultramarathon trail race in December. It would be my fourth race at that distance (32 miles). I recall that before my first ultra someone told me, "Every time I always think I can't do this. But then I just start." That's kinda stuck with me. It is hard! And it hasn't gotten any easier. But by focusing on what you will have accomplished at the end, I've learned to enjoy the toughness more. Having a mantra can help. I sometimes use these:
"Remember, you paid to do this."
"This isn't something I have to do. It's something I get to do."
"The body can achieve what the mind believes."
"Don't think about it. Just do it."
"Don't worry about getting to the last mile. Think about getting to the next one."
Here's a final (weird) piece of advice. Pay attention to what your face is doing. Are you always grimacing? Try to relax it or even go for a slight smile during the hardest parts. You face doesn't just show your emotion. It creates it too.
I guess the point I'm rambling about is that consistency and patience are the biggest factors to seeing positive growth in your life. Find a style of exercise that you enjoy. Then just stay consistent with being active. One quote I like is, "It never gets easier. You just get better."
Have a lovely evening!