Common Ground is More Solid
Art schools help students push their personal boundaries and risk new styles, techniques, and aesthetics. While this is surely why we go, and is the reason we really learn things that will lead to a career in art, it can also be very difficult, even humiliating at times.
That's why it's so important to develop supportive relationships in art school. The personal challenge of creating art is something only another artist can understand. There are a lot of things that can keep friendship going, but a common artistic pursuit is something unique unto itself.
Art Friends: An Honest Shoulder
It's nice to have some people to commiserate with, but it's also nice, years later, when you can commiserate at a comfortable distance! These long term art buddies are more than friends -- they're the people who can tell you when you're a genius (and you believe them), but can also tell you when you're "way off" (and you believe them).
At some point you'll need them to remind you why you wanted a career in art, and you'll need them to convince you to continue. But mostly, you'll need them to have someone to talk to who can really understand what you're aiming for in a project -- and we all know that for as warm as our mothers can be, they don't always get things like the abstract modernist movement.
Art School Friends Fuel Creativity
Art schools are hot beds for creative activity, and there's no doubt that you'll meet people that feed you and your work in a variety of ways. But keeping up with those people afterward will help too, as you navigate your career in art.