Knowing what to do and actually doing it are two different things.
Eating healthfully is a skill.
Exercising is a skill.
Changing lifestyle habits (sleep, stress, etc) is a skill.
And as with all skills, change doesn’t happen overnight or without effort, consistency, and persistence. You didn’t learn how to ride a bike in just one go, did you? Or without using training wheels to start?
You had help, tactics/tools (training wheels), and practice to learn how to ride a bike. It took time and a lot of wobbling and falling down before you got it right.
To be successful with our health and fitness efforts we need to accept and even embrace the long, winding path it takes to get from A to B. We’ll probably screw up a lot, backslide, and get frustrated from time to time.
It doesn’t mean that we suck or the effort isn’t worth it in the end. It means we’re trying. And that is what it takes to hit our goals. Learning and practicing the skills of healthy eating and exercising consistently, along with how to bounce back and make it work despite obstacles and less than perfect conditions.