I applied this rule to tape measures, because I found I never had one when I needed one, e.g., out in the car. So my new rule became: if you can't easily find a tape measure when you need one, buy another one at your earliest convenience.
Now I have one in my work bag, at least one in the car, one in my main toolbox, a few hiding around other places in the garage, one in the kitchen, probably one upstairs, on in my desk drawer, etc.
I did the same thing when Dollar Tree started stocking tape measures for $1.25. I figured that they’ll be accurate enough and I do need to measure stuff a lot, so I have ended up buying four.
I also have a keychain one that lives on my house keys, which has come in handy a few times (even if it is limited to 6 feet).
I applied this rule to microfibre cloth for my glasses. I bulk buy 100 of these online and place one each in every jacket I have, plus a few more around drawers at my home
Now I have one in my work bag, at least one in the car, one in my main toolbox, a few hiding around other places in the garage, one in the kitchen, probably one upstairs, on in my desk drawer, etc.
No regrets. Life is better now.