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.

No regrets. Life is better now.