What is the ‘rule of 3’ to save, how to adopt it in your life?

After the necessary expenses, 30 percent of your earnings can be spent on those things, which are not necessary, but gives happiness to the mind.

Such as watching movies, eating outside, painting, buying books or spending on any of your hobbies.

This part gives you the freedom to enjoy life, but living within the boundaries. This neither affects your savings nor necessary needs.