When will I learn to leave well enough alone?

So my toilet breaks and I have to call the plumber because the water won’t stop running. While he’s here fixing the myriad things that turn out to be wrong with it, I ask him why the seat always seems warm, like hot water is flowing in. He said that something that separates the hot and cold water flowing into my pipes was probably breaking. He fixed it. So now, when I get up in the middle of the night to use the toilet, instead of a nice warm, inviting seat, I get a cold ring of plastic.  And I have to wonder why I thought it was a good idea to pay to get the problem fixed when, in retrospect, it really wasn’t all that big of a problem.