Start at the top
At first glance it is a gray-brown avalanche of broken planes, and it is tempting to give up. Don’t, there is a man in here, and finding him is the whole pleasure. Start at the very top. That patch of fine diagonal hatching, almost like wood grain, is hair: wavy, carefully combed, parted on one side. It is the easiest foothold, so plant your feet there first.
Drop down a little and a face assembles itself out of the rubble, two dark almond eyes, the ridge of a nose, the line of a brow. Below them, a thin dark mustache sits over the mouth. Keep going down the center and you reach the throat, where Picasso has left two of the clearest clues in the whole painting: the neat triangle of a tie knot, and, swagging across the waistcoat, the little chain of a pocket watch. Those two ordinary gentleman’s details are the painting telling you, quietly, that this scaffold is a person, dressed for business.
Now the bottom. A cluster of pale interlocking blocks resolves into a pair of clasped hands, folded in his lap. And off to the lower left of the canvas (which is the sitter’s right side, since he faces you) sit the shards of a small still life: a bottle, and most likely a glass beside it. So Picasso pins the figure down top and bottom (hair up here, hands down there, watch chain anchoring the middle) and lets everything between explode into facets.
Why it stops short
This is not abstract art. Picasso could have dissolved Kahnweiler into pure pattern and walked away, and he chose not to. Analytic Cubism deliberately keeps a tether to the real world: just enough hair, eye, mustache, tie, watch chain and bottle that a patient viewer can climb back to a man. The painting’s whole charge lives in that tension, a face on the knife-edge of vanishing, held back from the drop by five or six clues a stubborn eye can still find.