When you focus on the past (positive or negative), you're creating inertia. That's what habits are. They require effort to get started but then require minimal effort to keep them going.
If you want to change your future, you're potentially fighting inertia, just like when you're driving your car. If you're going forward fast, it will take effort to get the vehicle to turn. If you try to turn too quickly, you're not accounting for inertia, and you will crash. Instead, you need to take the turn gradually. The faster you're going, the more gradual you'll need to turn.
As someone who doesn't have a lot of patience for change, I need to remind myself of this reality. If I try to change something in my life drastically, there is a good chance I won't be able to sustain the change. I'm turning too quickly and driving too fast. It's a recipe for disaster.
It's been a goal of mine to start my own business. Over the summer, I was in multiple classes, trying to learn what I needed to do to start a business. I was also working on development side-projects, my full-time job, fathering my daughter, figuring out a weight loss strategy, reading several books, trying to take notes on all these books and courses, and burning out in the process.
When I put everything on hold and realized that I needed to focus on a few things first (job, daughter, and weight loss), I started getting traction. When weight loss got enough inertia, I was able to add Ship 30 for 30. I have nine more days to go then shortly after that I'll close on my house.
I'm sustaining my changes because I slowed down and decided to work with inertia instead of fighting against it.