The 3 year itch of soccer: is that a "thing"?

Is there such a thing as the 3 year itch of soccer? Like the claimed 7 year itch of a marriage?

There is some evidence for this, and some counter examples too. 

Zidane did just under 3 years at Real Madrid. Won many wonderful titles and then decided to leave, stating that he didn't feel the team would be able to win next year. Mourinho typically stays for 2 years, of success, and then either leaves or goes thru a 3rd year of misery. And so far, Guardiola also doesn't stay around for too long. 

Futebol Clube do Porto never keeps a coach for more than 3 years. And is successful, for the most part. Barcelona FC also changes coach frequently. And is wildly successful. Real Madrid, likewise. 

Arsene Wenger stayed for 22 years and that turned out to be a flop.

But, then, Alex Ferguson held on for 27 years. And that was a major hit.

And, yes, there are many other examples of long tenures but ... as a general rule, is there a sort of 3 year itch of soccer when it comes to coaches? I have the impression that, in general, most successful soccer coaches win in a team for only a few years and then are "forced" to move on and be successful somewhere else.