Simple hack to spend less

It’s a very simple hack, and will also develop your math.
Suppose you pay 30% tax on your earnings. That means, if you earn 100 bucks, you pay 30 bucks in taxes. Your net earning is 70 bucks.
Now, whenever you spend, why not add the taxes you have paid to that amount? For example, you want to spend 10 bucks to buy something. Instead of considering the cost as 10 bucks, why not consider it as 13
This means the gross cost of the item you want to buy is 13 bucks
Why did we do this? You have to earn 13 Pay taxes. And then be able to make the purchase of 10 bucks. You have to work to earn 13 bucks. Not 10 bucks.
It’s a mental accounting hack. I learned from “The Art of The Good Life” by Rolf Dobelli. If reading a book is a difficult task for you, well I'm here for you. to simplify it. Do follow for more.