Is the saying: "If you can't buy two pieces of something at a certain time, you shouldn't buy it" a reliable saying to follow throughout your life?

Hello everyone,

I'm a 17 year old and my parents have made really bad financial decisions in the past - and this has made me somewhat careful with what to do when I turn an adult.

As the title says, if you don't have the money to buy two pieces of a certain item, you're better off not buying it. How many of you would suggest following this sort of statement?