I just moved into a house with a few friends. This morning, one of the "flexible" hoses under the bathroom sink decided to let go. Water only ran out for 30 seconds or so, but it still made a mess. We are very fortunate that we were home  when this happened. I bought two steel braided hoses to replace the broken hose, as well as the one next to it. While replacing the second hose, it broke off in an identical manner as the first hose. I'm thinking that all of the other sink hoses are getting replaced tomorrow.

TL/DR: Old hose broke.

I'm not sayin' it's poltergeists..

But it's poltergeists.

Unless you like sloshing across your carpet, braided is the only way to go. Something like that upstairs can wipe out a two
story house in a half hour.

I woke up one day, and decided to go into my basement on a whim.  I heard what sounded like sizzling.  I couldn't figure out what it was, at first.  I went into my laundry area, and after a minute of poking around, I found that the braided like coming from my water heater had sprung a leak on the back, by the wall.  The sizzling sound was a jet of hot water shooting out of the small fissure in the plastic under the braided sheath, and hitting the wall behind it (which separates the laundry area from the rec. area).  The wall, and baseboard warped slightly.  Had I not gone in the basement, I don't know how long it might have sprayed the wall, and how much damage might have occurred.

So, even braided line goes bad.  Lines are cheap, so replace them every once in a while.  It beats water damage.

Duct tape it.

We had a supply line to the toilet fail in our office a few years go. It is a good thing that I showed up at 4:30am since about a quarter of the office was flooded. Normal start time is 7:00am. The office would have been a mess had I not shown up early.


Weird.

Inspect your clothes washing machine's supply hoses, they are usually forgotten until there is 1" of water everywhere.

FloodStop valves are the answer.  Leak sensors are cascadable and, if you put one on the house supply line, the ability to turn the water on & off for maintenance is an added plus.

This is excellent advice. People forget that flexible hoses don't last forever. If you replace them, get the ones with the braided stainless steel on them. They won't last forever, either, but are more durable.