When a teacher asks a question and one confident person answers, everyone else can remain invisible. Peer instruction makes more people think before the answer becomes public. Each learner chooses an answer, discusses it with someone nearby, and answers again.
The individual–discussion–individual sequence matters. It gives people an initial position to examine and a reason to explain their thinking, rather than merely copying whoever speaks first.
The disagreement is the lesson
Imagine a workshop asking which of two proposed surveys would better answer a particular question. Neighbors who choose differently have something precise to discuss. One may notice a biased sample; the other may have spotted that the apparently better survey asks about the wrong outcome.
The instructor then examines the reasoning, including common mistakes. A change in the vote is informative, but agreement alone does not establish understanding: the most persuasive person could also be wrong. Asking why answers changed exposes more than counting the new totals.
Question design carries much of the work. If a question only asks for a fact someone either remembers or does not, discussion may add little. If it is incomprehensible, peers have nothing useful to compare. A well-chosen conceptual question creates a small, manageable disagreement that learners have enough knowledge to investigate together.