There's an old career adage that says people don't leave companies, they leave managers.

While that conventional wisdom may be true in some cases, people actually do leave companies — especially if they aren't given opportunities to advance their careers. At least that's what 7,350 LinkedIn members across five countries said in an "exit survey" of professionals released Tuesday.

The survey, conducted by LinkedIn, found that the No. 1 reason workers left their jobs was because they wanted greater opportunities for advancement.

There are two things interesting about that finding. For one, it means many workers may not be aware of the formal programs their companies have in place to promote and retain people in-house. Another recent LinkedIn survey found that 69 percent of human resources managers in the United States said employees were well aware of such "internal mobility" programs, yet just 25 percent of the departing U.S. employees in the new survey said they knew of them.

Also noteworthy is that of the respondents who stuck around and changed jobs within their companies, more than two-thirds said they found out about the job through informal chats with coworkers, such as meeting up for coffee. That's either further evidence that employees aren't aware of formal retention and advancement programs at their companies, or are electing not to use them.

Finally, what's also interesting is that other recent LinkedIn research found that the No. 1 reason employees (those not actively seeking a new job) said they'd be willing to head for the exits was for better compensation or benefits. That's different than the biggest reason most actually did leave, which was to take a step up the career ladder.

Meanwhile, the desire for a better relationship with one's direct boss didn't rank very high. Matt Grunewald, the LinkedIn research consultant who managed the study, said in an email that three times as many employees cited “lack of advancement opportunities” over “poor relationship with supervisor” as their top reason for changing employers. Though "better leadership from senior management" came in second among reasons departed employees chose to leave, a better immediate supervisor didn't make the top five on either list.

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