2.15 All is misery to the wise because of the pains of change, anxiety, and purificatory acts.
One thing in life we can always count on is change. If we expect things to stay the same, Sutra 2.
15 states that we will experience the pains of misery. In Yoga, the term Ishtah Kala roughly translates to "soul trapped in time". The nature of time, space and matter is change. At it's very basic level, our consciousness does not change, but we only see the change because we are conditioned to be part of the change.
One of my favorite toys when I was a kid was the Etch-A-Sketch. Looking back on it, it really wasn't the greatest thing. I mean, how far could you get making a picture without being able to draw diagonal lines. If you could even get the line to become diagonal, you would have had some sort of super skill working both those drawing knobs. So in school, I would make a drawing, and it would inevitably get erased by the other children. Gone was my masterpiece in mere seconds.
As we go through life, there is a natural tendency to try to maintain what we have. I think the more we get, the more time we have to spend maintaining it. I don't know how many times I have went to the gym to try to lose weigh, enhance cardio or gain muscle mass. Even when I have established a meditation routine, I would try to cram in as many techniques as I could.
I could only run for so long before my knees would hurt. When I got to a weight I could not lift past, I tried using supplements, but in the end, my elbows became inflamed. I got very good at doing various yoga techniques, but I wasn't until I concentrated on one, that I got the most out of it. A technique will outlast it's usefulness after a while.
You can only go so far in life before you top out at something. Sutra 2.15 gives us a work from the wise. Know that you can count on something not staying the same. When you top out, try to move on or teach what you know.