Dark social describes discovery that tracking can't see: a link shared in a private chat, a podcast mention, a recommendation from a friend, a video someone watched without clicking. These visits often arrive as direct traffic or branded search.
Self-reported attribution simply asks: "How did you hear about us?" The answers are imperfect (people misremember), but they capture channels that click data can't. The most useful practice is to compare the answers with click attribution for the same customers. Where they agree, you can be confident; where they don't, you've found influence your tracking misses.