The Law of Relativity states that things are neither good nor bad, big or small, expensive or cheap, etc. until you relate them to something else.
When something crummy happens in your life you can choose to relate it to something horribly bad and then your circumstance doesn’t look quite so awful.
If something (like eating well ) seems expensive to you then compare its cost to the price of getting well from a disease caused by poor eating.
Everything in your life and every decision you make is either a good or not so good choice based on the experience or object you compare it to.