If a tool is too rare or valuable to replace, then I won't borrow it. I'm willing to take the risk so long as I can afford to. The gamble being that you might end up buying the tool and never using it, which is the exact opposite of the whole point of borrowing something. So it's a calculated risk.

However, I also feel like the kid's shows are right and sharing is a critical function of good society. I'm not saying that society's biggest problem is sharing, but I feel like it is one of the easier problems we can directly address. And I feel part of that is producing more participants on both sides of the coin. So I'm not afraid to ask to borrow certain things, because I believe being responsible with that request is a tiny way for me to do my part to promote more sharing in general.

Besides, one of the weird little quirks about human nature is that we seem to like people whom we help more than the people who actually help us. And that's kind of weird from a self-preservation standpoint. But maybe that's a feature, and not a bug.