Starting a business can be a chilling experience. It can be isolated work; you lack a secure income for a period; and your personal life can suffer. It is therefore bewildering to note that some people not only start a business from scratch and watch it succeed, but they push off to start another. And another. And sometimes more.

So what makes these serial entrepreneurs tick? A lot depends on motivation. In The E Myth Revisited, Michael Gerber quickly identifies a huge subset of entrepreneurs who fail. Their reasons for starting up are more to do with changing jobs than anything else, and once they're up and running, they fall over quickly. There are a very distinct set of skills involved in starting a business - and not everyone has them.

Robert Drew, business angel and business group TEC's chief executive for Europe, Middle East and Africa, points to a number of characteristics the typical start-up junkie is likely to have. The first: "huge self-confidence and a willingness to succeed above all else. They're not too worried about details or the professional procedures within an organisation."

This isn't to say entrepreneurs are lax, but if someone is unduly concerned about which form needs to be filled in to requisition paper clips, or the size of their desk and the view from their office window, they're unlikely to have what it takes to start something up from nothing.

It's not unusual for someone starting a company to be young, not least because, if they're wise, they'll want to put in their own capital as far as possible to avoid losing control later on to people whose interest is solely financial. That's not to say older people have not succeeded spectacularly - Colonel Sanders of KFC fame was 72 when he began frying chickens.

"You've got to be willing to risk your own capital and, to an extent, your career," says Drew. "Once you're out of a normal career path and starting up a business, it's hard to get back in."

Other prerequisites include a lot of energy and total focus. "It's got to be a pleasure, not an irritation, when a customer calls you with a problem in the dead of night when you're on holiday," he says.

Drew, who is responsible for 10 start-up businesses, says entrepreneurialism is vital at the beginning of a business, and it remains so as a business becomes productive. As it progresses, he says, administration becomes more important and at this stage, the classic entrepreneur starts to lose interest.

People start looking inward at the business and what value they can gain from exiting, or whether they can score a good company car (or whatever tax-efficient substitute is around at the time). "That's what we call aristocratic decay," Drew says. At the early stages, people drink coffee from plastic cups. By the time the bone china comes out, the company is totally focused on itself and not the customer and invariably the entrepreneur will turn it over to managers.

"They turn the company around, but that's a different thing to starting up," Drew says. Yet another group come in once the business has been pulled back into shape - the professional managers.

So much for the life cycle, but what drives the entrepreneur and why do so many people start again? Janine Hawkins is on her second business, called Body Experience, a health spa in Richmond. She likes to take her own decisions and to be responsible for them, which isn't always possible in big business.

"Big business was good for me at one stage in my life," Hawkins says, adding that she worked in the financial sector in Australia then started an IT consultancy serving the same sector so that she could say what the business did and what it didn't. "That was in my 30s. I'm now in my 40s and am interested in my lifestyle." And her current business reects this.

But not everyone looks to start up a succession of companies. Bob Jones, managing director of Equiinet, is on his fourth business but he didn't set out to work in this way. "It's all been very positive. People come to me and offer me money for my businesses," he says.

Unlike a lot of start-up specialists, he's not proprietorial about these things. "I own about 30% of the current company. I'm not one of these people who has a hang-up about owning the majority every time."

He agrees there's a view that suggests you can be the wrong person to run a company day to day if you're an entrepreneur. "I suppose I'd have to say I've never been tested in that way, but it's all been very positive."

The sort of entrepreneur a person is likely to make does seem to come down to the sort of person they are. "One definition I've seen of work is 'something you do while you'd rather be doing something else'," Drew says. "On that basis, I've never done a day's work in my life."

David Abingdon, the brains behind four start-ups including business advisory company the Quantum Organisation (www.quantum.co.uk), of which he is managing director, had a similar realisation when he made work his hobby. Each of his companies has been hitting millions within the first year, but he still felt the need to move on.

Abingdon tried to analyse this against his council-at background. He moved to Australia to get away from the limitations he felt he had because of his background, and he concluded that he just enjoys the path he has chosen. "I accomplished something, it went well and I just got bored and moved on," he says.

All of this makes rapid-fire business beginners sound easy-going and not very hard-working. Nothing could be further from the truth. Abingdon made himself a list of things he'd like, including a house on a hill, pilot's licence and prestige car - and now he has them all. But there has been a cost. "You can do it all if you're laser-focused and don't listen to the people who say you can't," he says. "But you have to accept that things like holidays, Christmas, weekends and sometimes evenings are for poor people."

So a relationship is unlikely to survive, right? Actually not right, says Drew, and after 35 years of happy marriage, he's probably well placed to comment. "Your choice of partner is very important," he says, which is true normally, but even more so when you're dealing with the start-up addict.

"I've picked up three nationalities on my travels - some partners wouldn't have put up with that," Drew says. "A lot of people like staying put, and it's hard to see how they could if their partner is successful as an entrepreneur. They'll almost inevitably have to spend some time overseas."

Once someone has start-ups in the blood, they're unlikely to stop. Jones says that at 57, he's probably done enough, but won't rule out any further new businesses since he didn't plan to start up the first four.

Meanwhile, Drew actually tried to retire a few years ago. "I sold my businesses in Australia and did this and that for three years, came back to the UK and bought the boat - then got bored and started again." It's like a drug to him, he says. "I just love making deals."

Other elements combine to make every entrepreneur different. Hawkins talks about looking for some sort of perfection. She admits that it's not going to happen, but derives enormous satisfaction from bringing a business, and particularly its people, to their full potential.

Abingdon falls back on the image of work as a hobby. He does keynote speaking and at one seminar asked for a show of hands of people who had hobbies. A selection of hands went up. "Then I asked them to keep their hands up if they wished they could spend more time on their interests, and a lot of them stayed up. I think if you can turn yourself around and regard your work as the thing you feel passionately about, you'll succeed."

Interestingly, Abingdon doesn't see himself starting up again, because Quantum offers him scope to acquire other organisations and get the varied stimulation he'd normally get through moving on. But the company will remain the classic labour of love for as long as he can envisage. "I don't believe I'm getting paid for this," he says.