I am irritated at myself for forgetting my Rule.

"If lacking a special tool means you have to send a bike to the bike shop, always buy the tool and do the job yourself. You may spend a little more, but you'll have the tool, usually it will pay for itself the second time you do the job."

This time I needed to overhaul my bottom bracket, it is an old Stronglight, I don't have the 23.3mm puller, so I took my bike to the shop. It will be $32 to overhaul. Turns out the tool costs $55. So unless I will never need to remove an old Stronglight crank again, I should have bought the tool.

Do you agree with this Rule? Are there cases where you do not? Do some tools not pay for themselves despite a reasonable amount of home use? Facers perhaps?