Walk around Berkeley in a coat and tie--or even lose the tie and walk around in a tweed jacket with shiny black dress shoes, a button-down shirt, and dark well-pressed wool pants--and you carry your own cone of silence and zone of insulation with you. People approaching you part so as to pass at least three feet from you as you go by. People talking animatedly get quieter and quieter and finally fall silent until you have passed..
Walk around Berkeley in white tube socks, sneakers, running shorts, and a t-shirt, and the experience is very different--particularly if your running shorts have a three-inch rip in the seam caused by catching them on a pole as you jumped over a fence in pursuit of America's Silliest DogTM, and if you are unshaven because you fell asleep nose-in-computer while you were working on a draft of a piece for Slate, had to finish it in the morning, and so ran out of shaving time. Then you appear to be one of those random souls wandering around Berkeley whose brain has been fried by too much time nose-in-Grundrisse or contemplating the poetry and drawings of William Blake:
"Oh, you should definitely take 101b!"
"Are you sure? After 1, 101a has been quite a shock."
"But the math in 101b is not nearly as ferocious. And the professor teaching 101b in the fall--he wrote the textbook. Do it!"
"I'm not sure..."
"Excuse me. I'm Brad DeLong. A tenured professor here at Berkeley with my office in Evans Hall. I'm teaching Economics 101b this fall..."
"How can I help?"
"Well, should I take Economics 101b? Or 100b?"
"It depends. Are you a person who finds math congenial? Are equations and mathematical concepts aids to your understanding? Or are they unpleasant obstacles you have to clamber over? If they are the second, you won't enjoy 101b. If they are the first, you probably will."