Windows 95 Setup would notice that a file it was installing was older than the file already on the machine and would ask you whether you wanted to keep the existing (newer) file or to overwrite it with the older version.
Asking the user this question at all turned out to have been a bad idea. It's one of those dialogs that ask the user a question they have no idea how to answer.
Say you're installing Windows 95 and you get the file version conflict dialog box. "The file Windows is attempting to install is older than the one already on the system. Do you want to keep the newer file?" What do you do?
Well, if you're like most people, you say, "Um, I guess I'll keep the newer one," so you click Yes.
And then a few seconds later, you get the same prompt for some other file. And you say Yes again.
And then a few seconds later, you get the same prompt for yet another file. Now you're getting nervous. Why is the system asking you all these questions? Is it second-guessing your previous answers? Often when this happens, it's because you're doing something bad and the computer is giving you one more chance to change your mind before something horrible happens. Like in the movies when you have to type Yes five times before it will launch the nuclear weapons.
Maybe this is one of those times.
Now you start saying No. Besides, it's always safer to say No, isn't it?
After a few more dialogs (answering No this time), Setup finally completes. The system reboots, and... it bluescreens.
Because those five files were part of a matched set of files that together form your video driver. By saying Yes to some of them and No to others, you ended up with a mishmash of files that don't work together.
We learned our lesson. Setup doesn't ask this question any more. It always overwrites the files with the ones that come with the operating system. Sure, you may lose functionality, but at least you will be able to boot. Afterwards, you can go to Windows Update and update that driver to the latest version.
Note, however, that this rule does not apply to hotfixes and Service Packs.
[Raymond is currently on vacation; this message was pre-recorded.]