I've been a programmer for many, many years, and I see a problem all the time in modern systems that I don't understand: the stealing of keyboard focus.
My question for the other programmers among you, is: why is a theoretically simple concept like "focus", difficult for operating systems to manage properly?
In case you don't know what I'm referring to, here's an example. You're typing something in one window, and then some other window comes along that pops open and steals your focus away. So now, your typing continues in a new context, where each key now has new meaning. Worst case, you happen to hit Enter, at the exact time something like a message pops open, causing you to "accept" something that you didn't even read.
I have seen this with every OS, with many different applications, and with different window managers on Linux. It is pervasive, yet it is aggravating, which suggests to me that the problem must be "hard" or it would have been solved already. Right?
Fantastic operating system. Shame it's dying.