I've been struggling for a long time with discipline : started exercising, but didn't last long before canceling my gym subscription. Couldn't commit to a diet. A bunch of unfinished side projects and ideas waiting for me to work on them. And a lot more.
I read a ton of self help books, tried many Todo apps and planning strategies, nothing seems to work. I couldn't create the necessary habits to change my life and become more productive.
This is a real problem, and I'm sure is faced by many people. I realised I'm wasting time and it's costing me a lot. If you could offer a solution that works, I would be happy to pay for it, up to 100$ per month.
Diets can work, but usually if they are intended to address a known specific health issue. Then specific diets, like keto, have a pretty good track record. But merely restricting calories because you want to be thin has a long and well established track record of being the diet version of that smoking joke: "Quitting smoking is the easiest thing in the world. I know because I've done it hundreds of times."
Some general principles that sometimes help without fully understanding why:
1. Less is more.
Get rid of extra stuff. Streamline your life. Go for a spartan lifestyle.
2. Try fasting instead of dieting.
It's not well understood why it works, but it seems to often be helpful with a variety of issues.
3. Cleanliness is next to Godliness.
Just getting rid of a lot of junk will move you in this direction, but also: clean your keyboard, try to reduce papers in the home, switch to nontoxic cleaners, etc.
4. Keep a journal.
What gets measured, gets done. A journal is a personal record of your life. It can help you see what is or is not actually changing.
Best of luck.