You know what I've noticed?
Just because I was doing something right last year... or last month... or yesterday... that is no guarantee that I don't have to worry about it today! I've been through this cycle so many times, but it always amazes me a little bit. First you learn how to do something. Then you have to concentrate really hard to make sure that you're doing it. Then it gets easier. Then maybe it gets so easy that you're like "oh great, I can totally do that now, I don't have to worry about it so much." Then you start thinking about other details in the posture. And then you wake up one day, months and months later, and go "uh oh... what the %$#& happened to my locked standing leg in standing bow pose?!" And boom, back to the beginning. It was SO obvious that I forgot all about it.
That's why we have to exercise CONSTANT VIGILANCE!!! (And yes, of course that is an intentional Harry Potter reference. But seriously.) You've got to listen to the dialogue word by word. Every time. If you realize that (uh oh...) your instructors might be leaving something out, then you have to remind yourself of it. Every time. Even (especially!) if it's something totally obvious that you figured out how to do ages ago. Like locking the knee. Like fixing the eyes. (I busted myself for slacking on both of those things this week.)
I practiced to a recording of one of Craig's TT classes one time, and he said something at the beginning that I loved: "Be patient, be passionate, be vigilant. No fear." I thought that was perfect. No fear...