Michele Tummino, an entrepreneur in California, once stretched the truth in a job interview. She applied for a sales management position that required familiarity with computers. Her interviewer asked, "Do you know how to run a computer?" she recalls. "I said, 'Sure.' " That wasn't the case. "I don't think I'd ever sat in front of a computer," she says.

She got the job but struggled to master her technical duties. She came into work early to try to teach herself how to use the system. One morning, a colleague discovered her crying in the office.

Ms. Tummino's predicament may not be uncommon. Many applicants go after jobs that are "out of their league" assuming they will grow into them, says Marc Cenedella, president and chief executive officer of TheLadders.com, a New York executive job search service.

"Americans are a nation of strivers," he says. "People believe they have to create their own destiny, create their own luck. Being aggressive and optimistic about what you can do with your skills" is part of that.

It's one of the trickiest balancing acts in a career: Stretching for a job without falling off a cliff. One of the main reasons people look for new jobs is that they want more responsibility along with higher pay that usually goes with that. But there is a fine line between stretching just enough and too much. It's a dilemma not just for job seekers, but also for the hiring executives.

Karen Armon, an executive coach in Littleton, Colo., advises clients to ask themselves three questions to determine whether a prospective job is too much of a stretch. First, can you "ramp up" in 30 days? "The honeymoon is no longer 90 days, it's 30," she says.

Second, assume you won't have subordinates or colleagues to lean on. Do you have enough people in your own network of contacts to help you?

The third test: If you're switching industries, are you sure you can apply your prior experience to this new field? If you can answer yes to all three, "you've got enough stretch to be able to do it," Ms. Armon says. "If one of them is no, it's above you."

Often, people apply for "stretch" jobs because they're confident they can master more responsibility if given the chance. A 25-year-old information-technology manager in Northern California, who asked that his name not be used because he doesn't want his current employer to know he is looking for a new job, says he has applied for some positions seeking 15 to 20 years of experience. "I'm applying for jobs that I really feel that I can do but someone on the other end might take a look at my résumé and say, 'Well, I don't know,' " he says. "I'm taking a long shot but I know if I'm able to get into an interview I can turn the tables." He points out that he has been working with computers since he was a teenager.

He's trying to jump up the ladder because he feels stalled in his current job. He manages 24 people at a government agency, but doesn't see much opportunity for advancement. Over the past six months, he's applied for about 75 positions, about half of which are a notch or two higher than his current post. So far he hasn't gotten an interview.

People who have landed jobs that are a stretch often rely on other people to help them. That strategy worked for Eric Bowles, now a 46-year-old consultant in Atlanta. While working for Bank of America in the mid-1990s, the company asked him to manage a big technical project involving the development of new sales software and rollout of networked personal computers to 2,500 people. Mr. Bowles had a strong sales background, but not much technical experience.

Right away, Mr. Bowles realized he needed help from someone with the technical knowledge he lacked. He discussed the issue with a senior technology executive at the firm and they agreed that he would be assigned a deputy with technology expertise. "There's no way I was in a position to have all the answers," he says. " I needed something to shore up the area where I was weakest."

A generous colleague also helped out Ms. Tummino. The man who found her crying in the office gave her computer lessons. Her ability to overcome what could have been a disaster gave her confidence to tackle other challenges. She later took a job selling advertising in the Midwest for a Web site even though she had barely traveled outside California before. More recently, she started her own business.

"It all comes from taking that huge step of being able to say, 'No matter what, I'm going to make this work,' " she says. "It gave me the courage to fail. It's the fear of failure that holds you back."