Water seeks its own level. This means that when one pours a bunch of
water on a table it won't end up like a little mountain, but it will
very quickly spread out pretty widely (subject to surface tension,
etc.)

When you pour a lot of sugar or sand, or dirt it won't spread out as
much, I presume because of friction between the sugar, sand, and dirt
particles. If you have a box of the stuff and open a door at the
bottom, some of the stuff will come out the door

What about air?

If you have a heated building and open an overhead door 12 to 16 feet
high, for trucks, how fast will the cold air outside pour into the
building, and how fast will the hot air nearer the ceiling be forced
out.

I was recently at such a building, when it was below freezing out, and
I was close to the door and every time the door was opened, I'd feel a
bit of cold air, but not as much as I expected, and when the door was
shut, the building seemed back to normal very quickly. If it had been
full of water, in a twentieth of the time it took a car to drive in or
out, all the water would have run out. Does air not flow even at
1/20th the speed of water? What am I missing?