The drawing that taught me value. Not shape, not proportion — value.
Everything convincing in an eye lives in the contrast: the darkest dark is the pupil, the brightest bright is one small catchlight, and every other tone has to be squeezed carefully in between. The sclera looks white until you put an actual white next to it and realise it is a mid grey with a shadow arcing over the top of it.
The lashes are drawn as flicks from root to tip, fast, so they taper on their own. Slow down and they turn into wire.