Plateaus, for those of you that may have forgotten your basic physical geography, is "a usually extensive land area having a relatively level surface raised sharply above adjacent land on at least one side". It can also mean "a relatively stable level, period, or position." The verbal form (which also works) is "to reach a level, period, or condition of stability or maximum attainment". Either way (and both work for the purposes of my discussion) it's a flat place which, while raised, is not continuing on any upward path.
Why do I feel I've plateaued? Because in so many areas of my life, I simply seem to be. I'm not really moving forward (at least in any measurable way I can notice); instead, I am at the same level I have been for some time.
Why is this? Is it because I've accepted the plain as the end of the journey when there are mountains in the distance? Is it because I have failed to realize that the journey continues on a dog leg, while I am sitting looking at the cliff, having missed the turn? Is it because it requires a new level of effort and I am simply lazy? Or perhaps that I have become too comfortable here on the plateau: it's flat, it's easy, and I already know all the routines.
Perhaps all. But life cannot be lived on a plateau forever - because plateaus, given time, wear away. It's either up the mountain or back to valley.
(HT to artofmanliness.com for their excellent article "Plateau Busting: How to Take Your Life to the Next Level", which got this thought train started.)