What often comes to mind when we think of frugality is the act of conserving limited resources.
Fair use is planning from experience and foresight in proportion to the common problem in a 1/1 ratio, or acquiring something of value for far less than its worth.
Here it makes sense to be frugal. Running out of something important like money or food qualifies, and so does replacing something used every day like a pair of boots for better ones at a low price.
Faulty use on the other hand is when a need for absolute control, goes out of control, leading us to stockpile doubles upon doubles of various things.
Think of it as something a hoarder might do, like buying 4 microwaves of the same make and model in case one breaks or keeping expired food as emergency rations.
From the outside good from bad seem obvious, but to the person deciding it can be pathological, causing correct going from fair to fault without ever knowing it.
To distinguish between the two in a moment of decision, we need to ask a single question- ‘Is the choice based on sound logic, or strong emotions?’
The more often we pause for this question, the better we get and reading our inner motives, and the better our life gets as a result.