To take a walk in a public park, on a college campus, or on a long suburban sidewalk is to commit yourself to a steady stream of oncoming encounters. When driving, you have the luxury of a de-humanizing steel encasement. Albeit while navigating a meta-anticipatory cyborg-ian stew: manically adjusting due to the multiplicative dangers onset after strapping erratic homo-sapiens into belching combustable beasts of steel.
The psychological barrier makes up for the bedlam, a wombic alternative to the hospital lighting exposure of the walk. During the walk you see another traveler and before their face articulates itself into unquestionable idiosyncrasy a subtle ripple is felt in the airy-fabric between you. This ripple demands immediate attention, it is not to be ignored. There are three strategies I have identified for proceeding.
The first strategy is feigning unawareness. Pretending the ripple was a mere cosmic aberration, thus muffling biology as it screams out interest in a 99.6%+ genetic clone.
The second strategy is direct acknowledgement. This is a fraught approach, as you must never, under any circumstances, smile and wave too early. Once made, recognition cannot be revoked until the counter-party has apparated from your periphery. Holding mutual-recognition with a stranger is unbearable after 1.5 seconds. After 2 seconds of this torture, you would be better off flinging yourself headfirst from the path.
The final strategy is the worst of all. It is half-hearted acknowledgement. The hopeful lift of the chin and the choked hello. In my experience, it is invariably met with a steely determined look of feigned unawareness by your passerby. Left without the life-givings waters of reciprocal encouragement, your bud of greeting shrivels and dies, and a part of you goes with it.