Dwarves are Beavers! Beavers, I tell you!

You know the old Tolkien concept that Elves and Dwarves hate each other? Well, they might.  But I think that many Dwarves might have a resentment for Humans.

Think about it. Dwarves are builders. It's in their bones, their blood, their genes. Every dwarf instinctively knows how to build mines, houses, supports, anything.
In game terms, all Dwarves have a 3 in 6 skill in Architecture. Most never go any higher. An adventuring Dwarf can go higher, but most don't.
So, a Dwarf who has spend the last 200 years building and expanding the family mine suddenly meets a 25 year old human who wanders around his life's work and says, "I like this place, but... here's a list of suggestions to improve it."
You see, a properly focused Specialist can start with an Architecture of 5 in 6 at 1st level, and 6 in 6 at 2nd level. And this can really burn Dwarves up.

You see, Dwarves are like beavers. Beavers can build dams. They do it instinctively, without understanding the hows and whys. Then some humans come along, see the beaver's dam, say "Huh." and then go build a hydroelectric power plant.
Now Dwarves, as sentient beings, can rise above their instincts and improve, but it takes experience, both in the "XP" sense and the "Living life" sense. They have to go out and see the world. See other forms of Architecture that others have built.

Halflings have the same thing with Bushcraft, but are generally too mellow to hold it against humans.