Part of the reason is, we don't actually parse letters individually, but the patterns of words/letter-groups, sentences and general grammar. Another responder

Part of the reason is, we don't actually parse letters individually, but the patterns of words/letter-groups, sentences and general grammar. Another responder mentioned the infamous Cambridge study. My Layman's take would be that the patterns are recognizable enough that the pattern-matching portion of verbal cognition can still associate them properly without conscious thought. And any "misses" are filled in or trained by contextual clues.