The Accepted Answer Is the Whole Mechanism
Voting tells you what is popular. Acceptance tells you what worked for the person with the actual problem.
Most forums rank answers by votes. Votes measure how many passers-by found something plausible. Acceptance measures whether it actually solved the problem for the one person who had it.
Only the Asker Can Accept
This is the rule everything else hangs from. It cannot be delegated, bought or awarded by a moderator, because nobody else knows whether the problem went away.
Popular and Correct Diverge More Than You Would Think
Roughly one accepted answer in six is not the highest-voted answer in its thread. Usually the popular one is the general principle and the accepted one is the specific fix that survived the asker’s constraint.
Acceptance Is What Makes the Archive Safe
Someone arriving from search three years later needs to know which reply to trust without reading forty comments. A marked answer is the difference between a useful archive and a pile of transcripts.
Coming Back Is the Etiquette That Matters Most
Seventy-one percent of our answered questions have an accepted answer, which is high and still not high enough. If a thread solved your problem, the two seconds it takes to mark it is the only payment the answerer receives.