Constancy

It's the transitions that are the hardest part. This isn't just true of kids, but you can see it there most readily. Just about the time you get them set down and in their places, it's time to have them get up and move somewhere else. Stand in line, walk with your mouths closed. Now it's time to sit back down and talk. Then it's time for another quiet line that takes you to recess where you can run and play until the bell rings and you have to get back into a line that will take you back to a desk where you will repeat some of that prior behavior, unless it's Wednesday when you go instead to computer class where there are a whole slew of different routines and expectations.
Me? I tend to work best when there is a routine. Endless repetition is a strength of mine. I do not thrive amidst a bunch of transitions. It's different when you choose to pick up and move because you've finished a task or simply grown bored of the same old-same old. It's hard when you have those transitions forced on you. That's why this time of life is hard for grown-ups.
Relationships don't often end via some mutually agreed upon timetable. Somebody's attention span or fidelity is challenged and the wheels start to wobble. It takes a commitment on both sides to keep that thing rolling until it can make it to the metaphorical shop to be straightened out. Sometimes the wheels fall off and the relationship ends. All those routines and momentum stop. A new set of behaviors have to be installed in their place. A new set of lines, a new desk, a different group of people with whom you have to stand in line and sit next to in that new desk.
Some people thrive on that kind of experience. Some people prefer to change things up. Good for them. I'll be happy to continue in my well-worn rut, thank you. Change is hard. My sympathies to those of you who have been forced out of yours.