If you’ve been wondering when to leave your job, the answer is probably “within the next six months.”

But as much as we hear about how essential it is to change jobs every two to four years, the bottom line is that—subconsciously—this concept remains anathema to many people. It takes incredible discipline to get up and leave a pretty good gig.

But the reality is that business moves very quickly today—companies merge or sell, managers leave, service offerings change—and eventually that good gig will turn on us. If we don’t leave of our own will, at some point we will start getting hints that we are no longer wanted around—or worse. You are much more marketable as a job candidate when you are employed than when you are not.

The American workforce is in the middle of a long and painful correction period when it comes to job tenure. Perhaps a decade from now, the realization that we need to leave seemingly good jobs after two to three years will be internalized and may even be appreciated, but we’re not there yet. In fact, we resist it. Millennials and some GenXers seem to have gotten the memo while other GenXers and Boomers have not:

According to the most recent Federal Bureau of Labor Statistics employee tenure report, the number of years that workers had been with their current employer was 4.2 years in January 2016, down from 4.6 years in January 2014:

“Employee tenure was generally higher among older workers than younger ones. For example, the median tenure of workers ages 55 to 64 (10.1 years) was more than three times that of workers ages 25 to 34 years (2.8 years). Also, a larger proportion of older workers than younger workers had 10 years or more of tenure. Among workers ages 60 to 64, 55 percent were employed for at least 10 years with their current employer in January 2016, compared with only 13 percent of those ages 30 to 34.”

Why the disparity? Some of it is profound: many of us were raised at the tail end of an era when one parent worked at the same job until retirement. Although the world of work has long since changed, it’s difficult to shake the feeling that we, too, should be working somewhere for ten years, if not more.

Some is due to human nature: we’re hard wired to be comfortable and moving is no fun. Think of your home and the dreaded move. There’s the packing. The saying of goodbyes. The disruption. Not to mention actually finding the new place. Add a family and children into the mix and it’s even more difficult. That’s why we tend to live in homes for a long time. As a matter of fact, according to the National Association of Realtors, the number of homeowners staying put has been steadily increasing since the recession and now averages 10 years. That’s not necessarily a bad thing insofar as home ownership. For many, more years in an owned home translates to more equity.

But, unfortunately, the complete opposite is true at work. The longer you stay at a company, the more your “career equity” diminishes. If you wait more than four or five years to seek a new job, you run the risk of being considered someone who would have a hard time fitting in with a new company—and someone lacking drive.

Think about it. What new concepts and skills are you learning at your company after four, five, or six years in? It’s great to know everyone’s names, to understand the inner workings and politics of the company, and to have some seniority and extra vacation time, but that means little to the hiring manager. The hiring manager is looking for someone experienced, vibrant, driven, and flexible and those qualities do not transmit from candidates who have spent many years at the same company.

So, how do you know when to leave your job? Of course, it all depends on your industry, geographic location, and situation, but at about the 2 ½ to 3 years mark you should be actively looking for a new job. At this point you have established yourself, you present well as a candidate, and that you have not received a major promotion will not be held against you.

The most important thing you can do to proactively manage your career is know when to leave your job. It may seem counterintuitive, but it will mean increased wages, new stimulation and career security—and, once you get the hang of it—you may actually enjoy it!

If you need advice in when to leave your job and support in preparing for your job search, contact San Francisco-based resume writer, Robin Kelley, at Resume Preferred to schedule an introductory call.

If you’re a senior executive and are seeking to capture and convey your value in the marketplace—and achieve the next level of career success—contact Leadership Career Consultant Amy Phillip.