I would absolutely have written your post 3 years ago (ignore the faux wide eyed head tilt naivety that people don't understand ...its put on and dpointless). I would say it depends on the situation so here's mine.
Initially for weight loss I started running. Brilliant it worked. Stopped running when I had lost weight.
Had a stroke at 38 , started running after i was able to walk again (partly because it was a shock to the system and i got overexcited at even being able to run) to lost the 8 stone I had packed on , great it worked. Weight loss. Running officially took a backburner due to a divorce and lack of childcare but if I'm honest it stopped because I lost my goal.
Mental health took a giant wallop this year. I lost my job due to covid childcare , etc etc so I started running again to improve my mental health. That's my goal now.
If someone tells me to exercise for 30 mins a day because I should....
Nope I have bob hope. I just will not be able to do it.
I can't do exercise for exercises sake ever , i need a goal to work towards or i end up counting down time , focusing on the uncomfortable aspects. I am really goal driven so doing something without a specific goal feels really pointless to me. People rattling on about exercise being good for you does me no good.
What does help me is to have my own personal goal. My mental health goal has milestones just like the stones and pounds for weight loss but it stretches into years. (Actually a decade) .
Maybe you are the same. After a while though I found I went for a run because I felt like it , it just added progress to a goal but it was because I wanted to. Again that is starting to happen
Without fail though , the first few weeks are bloody horrible and I winger and complain in my head , I do think you have to power through the first couple of weeks with sheer determination (that's where my goal setting works because I refuse to fail before my goal....even when i really want to) ,after a few weeks you stop noticing the uncomfortable bits as you have moved a bit towards your goal and you don't want to lose that progress.
It may be completely different for you but that's the mindset that worked for me. I detest with every fibre of my being working out for no specific goal. I hate the first few weeks of working out. Once into the swing though , completely amazing and the one thing that keeps me sane.
Good luck OP