system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does jailbreaking technology exist? Why is there something for me to break into, instead of never having it there in the first place?

I asks because I just read an article about how hackers had figured out how to jailbreak Google Glass, as there had been some features that Google didn't want available on the glasses. But why do they exist there in the first place? If they didn't want them to be used, why are these capabilities still on the software? Hope this makes sense...
gpt
A digital watch is a computer, but it's limited. The computer hardware is designed to be a clock, and nothing else. There's no point in jailbreaking a digital watch. They're like a train, they have fixed rails they run on, and you can't take them off those rails, or they won't work.

But phones, tablets, computers, google glasses etc are "fully general computing devices", which means they can run any program. They're like cars - they can drive on any road, or drive offroad, or anything. Making a computer (or phone, tablet, glass etc) that only runs certain programs is like making a car that only drives on certain roads. You have to deliberately restrict it by putting up some kind of barrier, because by default it can drive wherever. Google glass can run any type of program, and if Google only wants it to run the program they put on there, they need to put up some kind of barrier.

Jailbreaking is figuring out a way to get the car over or through or around the barrier, so you can drive it wherever you want. You're not breaking in, you're breaking *out*.