You're trying to focus on your breath. Other thoughts arrive. You push them away. More thoughts. You push again. The pushing requires effort. The effort produces a narrow attention. The narrow attention feels like meditation is working. K would say: the narrow attention is the disease, not the cure. You've trained the mind to exclude. Exclusion isn't the same as attention.
K distinguished concentration from attention. Concentration is the narrowing — choosing one object and pushing away everything else. The pushing is the giveaway. Concentration requires resistance to what isn't the chosen object. The resistance is effort. The effort is fragment-work. The mind has been trained to be a smaller, more obedient fragment. K thought this was the opposite of meditation.
Attention, in K's vocabulary, has no exclusion in it. Attention is wide. It takes in everything — the breath, the sound, the body, the thought, the noise outside, the feeling that arose two seconds ago. Nothing is excluded. Nothing is preferred. The mind is available to whatever is present. Concentration is a narrow beam. Attention is the room with no walls. The first feels like discipline. The second feels like permission.
The body of concentration is tight. There's effort. The forehead has tension. The breath is controlled. The body of attention is loose. There's no holding. The breath finds its own rhythm. The mind doesn't struggle because there's nothing to struggle against. Concentration takes energy. Attention requires letting energy do what it does.
Concentration is exclusion. Attention is openness. Most meditation instructions train concentration. Most students think the concentration is the prize. K thought attention was the prize and concentration was the obstacle. Two different practices producing two different bodies. Easy to mistake one for the other if you've never had the second.