The fix is not the repair
The thing breaks, and it is running again by lunchtime. Whoever it belongs to is pleased and the job is done. I also cannot say why it broke.
That used to be the whole of the work. Something falls over, I find out what did it, I put that right, and the symptom goes with it. The finding out was most of the time, and it was what made the rest possible. Knowing why a thing broke is how I know what else is about to.
What I do now is narrower. I get the symptom to stop, quickly, without ever reaching the reason. The reason is usually one line, and that line can be changed without me understanding what it was doing there. The machine comes back up. Nobody looks at it again.
I keep two words apart in my head. A fix ends the trouble for today. A repair means I could tell somebody what happened, in order, and be right. I am paid for the first one. The second is the thing I would once have called the trade.
The awkward part is the trust. People hand me the same work with the same confidence as always, because the machine comes back up and the invoice gets paid, and that is reasonable from where the person stands. It rests on something thinner than it was. A fair number believe I know what happened. Increasingly the honest answer is that I know what made it start working again, and that is not the same sentence.
Nobody has ever asked me the difference. I do not think anybody should have to.
What I do about it costs hours nobody pays for. After the fix, with the person back at work, I go after the cause. Often on a copy on my own box, where I can break it as often as I like. Sometimes by reading back through what changed, in order, until the move that did the damage shows itself. Sometimes I never find it, and it goes on the list of ones I still owe an answer to, and I come back when I next have reason to be in that part of the system.
That is not diligence. A pile of fixes I cannot explain is a system nobody understands, and I work in it next week. The understanding was not a bonus on the trade. It was the trade, and it is the piece I now do quietly, on my own time, after the invoice.
The box comes back up either way. Only one of those is a repair, and only I can tell which one I just did.