All the mythologizing is so unfortunate. It has popularized badly misguided notions about how a CEO can succeed in a job that’s not only crucial to the economic foundations of our society but also so cognitively, emotionally, and physically challenging that nearly a third of those appointed last fewer than three years in the role. The mythmaking has obscured so many important lessons we can learn from observing how CEOs struggle mightily with the changing challenges of the role. And overcome them, not only in the early going but also throughout their tenures.

For two out of three CEOs in our database, performance was lower in their years six to ten than it was in years one to five. Some gave up their gains of the first five years altogether. Results may not actually dive into negative territory, but if they do, they vacillate up and down around a mean, which only reinforces the sense that one can let up on the gas.

The danger is exacerbated when boards also become less energetic in pushing for vigorous changes in strategy or operations. As director Ann Hanley shared, “It’s easy to get into incremental mode.” A CEOs internal team may resist a continuous quick pace of change.

When it comes to TSR over their full tenure, marathoners were hands down the strongest performers, accounting for eighty-eight out of the top one hundred. But when it comes to CAGR, the sprinters were the winners with forty-five out of the top one hundred. The mid-distance group trailed on both of these measures. These findings reinforce the observation that during the years of the Complacency Trap, years six through nine, CEOs’ performance may be less than stellar, dragging down the overall performance numbers for CEOs who stay on through those years.

Much less focus, however, has been put on the problem of more gradual deterioration, or stagnation, of performance. Our Life Cycle research reveals that this is a particularly common development beginning approximately after the first five years of a CEO’s tenure. Company performance was lower on many fronts in years six to ten for two out of three CEOs than in their first five years. The rate of revenue increase slowed in these later years. Both EBITDA and ROIC slackened relative to earlier years, companies often became less efficient, and growth in operating income stalled.

As former Intel CEO Andy Grove wrote in his influential book Only the Paranoid Survive, “Business success contains the seeds of its own destruction.” CEOs who make it to the Complacency Trap stage have navigated the rough-and-tumble of the Launch, Calibration, and Reinvention stages of the first few years. One unintended consequence of leading their firms adroitly can be an overly assured attitude about the course they’ve set and the organizational improvements they’ve made.