Change often comes when we don't expect it, from directions that surprise us.

Occupy Wall Street, the movement that's shaken the Manhattan establishment and spawned offshoots across the country arrives in Philadelphia today with demonstrations at city hall.

Mayor Nutter and team are inclined to be accommodating, which makes sense. Who's going to criticize young people taking peacefully to the streets, demanding that we value human decency over unbridled greed, all the while embracing democracy as practice, not just principle?

If you didn't hear Zoe Chace's s Morning Edition piece on how the New York protestors overcome the ban on bullhorns, you should listen.

There's a deep well of commitment and activism to be tapped here, and I expect this demonstration may be impressive.

But as somebody who came of age in the Vietnam era and studied history for a long time, I'm acutely aware of how often movements born of passion and idealism go awry – torn by factionalism, manipulated by special interests, or worn out by exertion without results.

And one thing that occurs to me about the Wall Street protest movement is that it's hard to define its goals.

It would be great to see some guys in expensive suits come out in handcuffs, but changes that will transform the way the financial system operate can get complicated.

The Dodd-Frank financial reform bill passed Congress more than a year ago, but most of the reforms aren't in effect because they require the drafting and approval of specific regulations, and special interests are in there fighting tooth and nail over every one.

This is from a June piece by Louise Story of the New York Times:

So far, 28 of the financial overhaul rule-making deadlines have been missed, according to Davis Polk, a law firm that is tracking the rules. Of the 385 new rules to be written, the law firm says, regulators have completed only 24 requirements; they were supposed to have taken 41 such actions by now.

''There's an attempt to kill this through delay,'' said Michael Greenberger, a law professor at the University of Maryland and a former official at the Commodity Futures Trading Commission, which is in charge of writing batches of the rules. ''The difference between eight or nine months and 24 months could be cataclysmic here.''

A more recent story says fewer than a quarter of the 400 needed regulations have even been drafted, much less approved.

If the Occupy Wall Street movement could get some public-spirited wonks and fashion an agenda it can throw its weight behind, it can have impact.

If I were active in the movement, I'd be thinking about how to sharpen its goals, so the energy doesn't dissipate.

Nobody knows where this thing is headed, but its arrival is welcome.

I know my friend Will Bunch at the Daily News will be all over this, and in a post earlier this week, he captured the energy and innocence of another age, with Jefferson Airplane's performance at Woodstock. Check it out here.