^^ I think I just wrote a novel!!!
This may come across as odd, but I never thought in detail about how straying true to my "chosen line" happens! For me a big part is seeing the road and knowing how its layout will affect the bike. As in, will the bike do what I'm asking of it or will it be upset and stray off course. In short if I predict properly, the path has been chosen and the bike and I are linked as one. Basically I expect it on the dime and it is "on a dime" unless I predicted wrong and DIDN'T take something into account. I'm not sure if that makes sense?
An example is this; In the corner ahead I see a dip just before the apex of the turn. If I hit that dip at speed I will be launched, be unable to turn, and I will go wide and miss my line (and likely miss the turn completely). So before I ever hit the dip I know how the bike will respond, I've anticipated where it will be after the dip, and I adjust before it happens which keeps me where I intended to be.
In short, can you accurately predict how your bike will respond to most events? If yes, you should be able to hold your line.
To learn and be ahead of the curve (our limits) I push the boundary before being backed into a corner and having to deliver. That is, I know what the bike will do if I pin it in 1st gear while leaned over (will it bust loose, will raise the nose, will we slide out, will it stand up, etc), if I lock the back tire, if I lean too much going too slow, if I don't lean enough in a corner, etc.. .. .. I try to equal the playing field by placing us as a pair into situations before it really matters so I know what to expect! Essentially testing the water before it gets too deep and I don't have the skills for the level I'm riding at. Does that make sense?
The other day it rained for the first time in months. I tried a panic stop, I tried hard rear brake stop, and I purposely dumped the clutch on a new tire while coming out of corner in 2nd gear at higher RPM's to see how far can I push it before all hell breaks loose!! So for me, its about knowing limits and NOT placing myself in a situation where I exceed my skills and jeopardize us. All actions are pretty much reflex and honestly, nothing rattles me as its all just a reflex. Please this is not me trying say I'm bad @ss, this is me learning something new when it presents itself. I'm pretty sure that hitting gravel at 70mph in a turn would have made me pretty uncomfortable two years ago. Tonight it happened about 3 times and I didn't think twice about. Yes, I aimed for the lessor concentration, yes the bike moved over (but I knew it would). I Neither over acted or under acted and the bike was exactly where I expected it to be. Obviously ALLOT of gravel would make me slow down. Scattered pebbles and the bike moves over a little but its OK as long as you don't freak out.
The take away: for me is prediction, expectation, and being smooth are my keys so as not to compromise us placing us in over our head!
I'm sorry, I can't condense it into something sensible but it has allot to do with knowing you limits, being confident, practice, repetition, looking ahead, predicting, hitting my target(s) based on what I know, being smooth, Not over reacting, and always work on keeping my skills fresh! I think there are times when I should have panic'd but that's only going to end badly so I just hang on and lean more! lol
I hope something I wrote adds value to someone.