I find that going too hard too early is demotivating.
If I nearly kill myself by exercising too hard, I certainly don't look forward to exercising again.
My father in law is just like you Serena, he's like a bull at a gate and burns out or gets injured very quickly and that defeats the whole purpose of exercising in the first place.
The trick is to start exercising at a very comfortable intensity so it's almost too easy.
Once it becomes a habit, gradually increase the intensity over time.
The only thing that this approach takes is patience, because the results may come a little slower than if you exercise harder from the outset.
Exercise is a little like compound interest, it builds on itself over time.
As they say, 12 months of easy walking is better than 1 week of running!
The secrets are to be patient and do what ever it takes to make exercise a habit.