Before retirement, it was hard to visualize what retirement would really be like. I had seldom even had any vacations much less extended time off. So, having read that truism, as we all have, I was kind of concerned that I did not plan to "retire TO something".
For me, that turned out to be complete and utter rubbish. I have had a great retirement and have no difficulty structuring my time without having something I am required to do (either by somebody else, or by me). If I was offered a billion dollars to come up with something I retired TO, I honestly couldn't tell you what that would be. And yet, my retirement has been wonderful. (Or maybe that's the reason why my retirement has been wonderful?)
But YMMV!! We are all individuals. My point is just that this truism does NOT hold for every retiree, not at all. I'm not even certain that it holds for many or most retirees.
Not me, unless you include getting that first cup of coffee as something that I set out to do that day. Gotta have my coffee.