What minor change massively improved your life?

I learned to validate myself.

Since there were many mentions of allergies, I should point out lactose intolerance. Everyone is lactose intolerant to some extent. Even if you continue to produce the lactase enzyme into adulthood it is in limited supply.

Its been good to learn that there is a limit to how much cheese I can consume.

Slightly tangental, but I learned that I was allergic to shellfish! I was wondering why I felt sick immediately after eating foods that were mixed with shellfish or contaminants. Knowing makes life a heck of a lot easier.

Edit: a bidet, to give you a better answer!

Stop rushing into relationships with others, learning to trust our gut about things.

Giving up gluten, turns out we were minorly allergic all these years and that was the source of our tummy pain, which doctors never thought to check.

Mentally seperating ourselves from those we live with.