PARIS -- It happens to a lot of people. They achieve career success, make enough money to live comfortably, and then -- bing -- they have a strong urge to: Pay Back.

This yearning to reciprocate -- heightened for many by the Sept. 11 attacks -- often manifests itself as a desire to go work for a non-profit organization.

But finding a job helping humanity isn't easy. And even if found, it won't necessarily be a picnic.

"It's not like they go to the non-profit world and it's all nice and all lovey-dovey," says Neil Janin, senior associate director at consultants McKinsey & Co. in Paris. "It leads to a lot of frustrations and emotional challenges."

A big change is the uncertainty about how to measure performance. As well as office politics complicated by diplomacy. Then there is getting up close and personal with suffering. Heart-wrenching.

Take Didier Cherpitel. A 56-year-old Frenchman, he is now secretary general of the Geneva-based International Federation of Red Cross and Red Crescent Societies, a job he won in 1999 after taking early retirement from a 27-year banking career at J.P. Morgan.

Sure, he finds this challenge immensely more rewarding than what he describes as the straightforward business of managing money.

But, he says, "It's tough. I have my ups and downs."

Now meet Philippe Lerch. Also French, he is director of the U.S.-based Surgeons of Hope Foundation and an affiliated French charity, which build heart surgery facilities for children in developing countries.

"If I had done this at a younger, less-experienced age I would have slammed the door behind me. I would have said, 'These people are crazy," says Mr. Lerch, who had a career in hotel development before opting for early retirement six years ago to take up this full-time job at 55.

New managers largely feel at sea at first because of this difficulty in measuring the performance of a non-profit organization, says McKinsey's Mr. Janin.

"You don't have a profit-loss statement. Instead it's 'I have something to give to you and you're not going to give it back to me."' Mr. Janin says. "It's a dog-master relationship. Dialogue is dead."

Indeed, Mr. Cherpitel says, he was stunned when he arrived at the Red Cross and, "I asked them what their goals were. They couldn't articulate them. I asked them about their strategic plan. They didn't have one."

Newcomers can encounter a lot of resistance to their ambitions of "professionalizing" the outfit, Mr. Janin says.

Hmmn, did Mr. Cherpitel?

"Yep," he says.

Mr. Janin explains: "The organizations think they have no need to be efficient. They are there to help people, they are not there to make money. They have an attitude -- 'I can't do bad if I do good.' "

He says newcomers also find that the work often is organized into too many never-ending projects implemented by an army of consultants. They travel in a world of perpetual conferences. They chat and chat. And nothing happens.

Mr. Cherpitel recalls his first assembly of the federation's 117 member societies: "For me it was a zoo all the time. I was on a very different planet."

Newcomers also must adjust to working with people who can be very emotional and partial to their own causes, Mr. Janin warns.

Indeed, Mr. Lerch says his challenge was taking a group of highly individual-minded workers and fashioning it into a 17-strong team. It took two-and-a-half years, he says.

Then there are those country politics.

Mr. Cherpitel says he gets frustrated with a two-faced attitude toward AIDS in certain African countries. (He declines to identify them.) "Being too good at lip-service and not at delivering," he says, "that makes me really mad."

Then there are the occasions when he has had to get a grip. "It is seeing a 20-year-old girl dying from HIV, with a three-month-old girl," Mr. Cherpitel says. "Sometimes it's tough not to let it affect me."

If after all this, you still are tempted to make such a career switch, Mr. Janin suggests you:

Aim to use your professional expertise.

Consider whether the job itself will be interesting. "If you are cleaning latrines, you won't do it long," he says.

Be practical. Like, should you really go to Chechnya with your now-jobless wife and young child?

Start at your church, or a community organization, he says. And try the idea out incrementally. Mr. Janin pays back through pro bono consulting for the Red Cross.

And before you try to take the leap, ask yourself: Do you really have what it takes?

Mr. Cherpitel is convinced he does.

"I'm passionate about it. I'm very stubborn. I want to make it happen," he says.