I bought my computer a new mouse. The old one had begun to double-click: you press the button once but it clicks twice. Actually it had been doing this for some time, but whap the thing a few times and it'd stop, for a while. But then the whaps stopped working. I opened it up, which I hadn't done before, and took out a wad of cat hair that had become wedged in, but that didn't stop the double-clicking either. It was just the most-used left button, so I was pretty sure it wasn't a software issue, just a very old mouse.
Actually it wasn't a mouse. It was a Logitech wired trackball, and so is the new device replacing it: fortunately they still make them. I've always preferred a trackball; they sit still on the desk and don't require room to move around, or friction to respond to. And wired, despite the nuisance: that means it's always physically attached to the computer and can't wander off, with or without feline assistance.
At about the same time an alarming software issue arose. I lost access to Outlook, which is pretty grim because that's where I keep all my e-mail. I'd quite recently run a backup, but that wouldn't help with subsequent arrivals. I closed the program and restarted it, but that didn't fix the problem. Before considering taking the computer in, I shut down and restarted that. And I noticed, even though I'd closed all the running programs first, that the shutdown said Outlook was still running and the shutdown program would have to close it. I bet that two copies of Outlook had somehow opened and were interfering with each other and that's what caused the problem, I thought. And sure enough, after the restart it worked fine.