system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Diabetes, please.

I understand there are different types, and I'm still struggling to understand it the difference between them and what exactly triggers it . I don't have it, but it seems somehow common.
gpt
Basically the issue with Diabetes is Insulin.  Think of insulin as a keycard, glucose(sugar) as you and your friends, and your body's cells as a locked room with a party inside.

Normally, you would use a keycard to swipe the reader near the door, the door then opens, and you and your friends walk into the room. In this way, insulin changed the state of the door (from locked to unlocked) and glucose(you) could then enter the cell(room) and keep the party going.

In type 1 diabetes, there just aren't any keys. There may have been when you were young, but somebody destroyed the keycard-making machine. Without you being able to get keys from elsewhere (insulin injections), you won't ever get in the room(glucose can't enter cells).
Without any keycards, no-one can get in and the party dies.

--This used to be commonly called "juvenile" diabetes as the cells which make insulin (located in the pancreas) were destroyed by the bodies immune system.

In type 2 diabetes, the keycards you have just don't work very well anymore, you sometimes have lost some, and the reader might have broken a little bit. So, sometimes the door opens and people can get in. The problem is so many people want to get in, that there's a line out the door. So, the party is still going, but all these people are sitting around with nothing to do, and start to go around the neighborhood, trashing the place.

--This is what happens in type 2 diabetes: you get sugar levels going way up since the insulin doesn't work so well at getting it inside cells, and these high sugar levels can damage other body tissues. We're not fully sure the exact way that this happens, but it seems diet and exercise can have an effect on it.