I'm a pretty simple fellow, and I like simple rules. I'm also a bit of a cheap bastard, and I don't like spending money that I don't have to. On the other hand, I like to think that I'm fairly self-sufficient, and I hate borrowing things. I hate wandering over to my neighbor to ask if I can borrow a cup of flour, an onion, his car, or that tool that I sometimes could really use. It actually irks me to ask family if I can borrow things...that's how screwed up I am! :)
So when I'm doing a DIY project, there are always times when a certain tool would be helpful, but I don't really want to buy it for a single-use. Sure: if it's a $3 tool, go buy it and even if you only use it once, it saved you an hour and that's worth the money. But what if it's a $50 tool? $100? I object to buying that tool, using it once and leaving it to sit in my mess of a workshop never again to see the light of day. I also object to buying the tool, using it, and returning it. My cockamamie sense of honor prevents me from doing that.
If I've only got this one job to do, I'll typically muddle through, even if it costs me a few more hours and a bit of stress.
So when do I break down and go out and get that tool?
The sentence is: “This job would be a lot easier if I had a !”
If I fill that blank in with the same tool three times in one month, I go and buy that tool.
I like this rule a lot. It's prevented me from buying tools that I don't really need, and at the same time it's forced me to buy tools that really come in handy somewhat often. If I were to need a specific tool once every half a year for five minutes, I might just swallow my pride and go ask a friend if I can borrow one. Or, I'll come up with a way to use not-quite-the-right-tool to get it done.
This rule forced me to buy my Rotozip, my chainsaw (when you need a chainsaw, nothing else will do), brad nailers, and a host of other tools that I really like having on hand. It has prevented me from spontaneously buying impact hammers, hammer drills, a drill press, a bench grinder, and countless other tools that I don't have room for, and that I would have used once and left in my already over-stuffed workspace.