Imagine living life as a frictionless surface. Imagine getting out of bed, letting your feet hit the ground, and eternally slipping...until you can grab something to stop you, correct? Chances are, your hand would slip as well. Friction is extremely important...and it makes our lives livable. The coefficient of friction of rubber shoe tread (on dry asphalt) is an astonishing .9! We don't notice it, but our shoes are very frictional. The MythBusters did a segment on friction when they busted of the myth of the "banana peel" slip commonly seen in cartoons. Although the myth wasn't exactly true, banana peels DO in fact decrease friction by a considerable amount...or at least enough to make Adam Savage look like an idiot in this clip:
Rubber is one of the most commonly available materials with a very high coefficient of friction, making it feasible for civilian clothing use. Its coefficient is maximized when contacted with asphalt, or any concrete surface (making rubber a great choice). However, metal-on-metal coefficients of friction are sometimes higher. When one examines the lattice structure of metallic atoms, small pieces of the other metal will be lodged into the other metal. No matter how smooth you make something (realistically), there'll always be tiny "welds" and "tears" on both surfaces.
Thank friction. Don't slip.