riding the white line

there are fine lines everywhere. hairline splits, delicate fractures, cracks that let the light slip in. we draw lines, we eliminate them, and sometimes we cross over them.
most often, it seems, they exist between one side and another, and we ride them. figuratively that is, though many cyclists I know ~ including this one ~ prefer to literally ride that white one as often as possible. [an aside for those of you who don't ride much: the white paint fills in some of the roughness of the asphalt and thus is just a titch smoother than the non-painted surface.]
back to figurative lines.
one exists between good pain and bad pain, and this line is wide and wiggly, and I am not comfortable with riding it. given a healthy body part, I can navigate that line pretty well. my heart, for instance, is wonderfully healthy and I know enough about it to understand when I can push it and when it becomes too much. it hurts along the way, but I know it's good pain. another example is my triceps: I can work them, fatigue them, make them scream, and I know it's all going to be okay. they won't become injured before I have to quit from sheer exhaustion.
it's those not-so-healthy body parts that cause me to question the line.
the other day I wrote that my right shoulder was healing so well that I might be ready to return to power yoga. this morning in "gentle yoga" my right shoulder told me otherwise. I have been playing the "positive thinking" game, exercising and stretching my shoulder, and trying to be gentle with it when putting myself in positions that may stress it. I've been telling myself for months that "my shoulder is getting better," and I pretty much believe myself.
but this morning it was talking to me. and I'm not really sure which side of the line it was on. at first I thought it was just letting me know it was there, ready to work, letting me know that I was asking a lot of it, but a manageable lot. and then after about the 8th visit to "cobra," I started thinking it was telling me something different. like, "you know, susan, I really don't want to do this anymore, and I might just start going backwards on this healing thing if you keep it up."
or perhaps it was just saying, "ow, this is tough, but each time you make me do it I'm getting stronger, so keep it up."

how do I know?
the line is amorphous, and I am adrift.

this is when one needs a professional, I suppose. I can positive-thought myself right over the edge sometimes, or I can wimp myself right out of any activity.
when I first went to dr. jamie to have him assess my shoulder, I couldn't stretch my right arm up behind my back much further than my waistline. but then he told me it was okay to push myself, using a towel held by my both hands, to pull that stretch further until I could get my hand more than halfway up my back. this hurt! but the doctor told me it was a good hurt.
good hurt versus bad hurt: the line between is where I ride, and knowledge of where to stay is what I reach for.