Talk ratio, the share of a call the rep spends talking, is easy to dismiss as a vanity metric. It is a single number, it is easy to game, and a great call can break the rule. But on discovery calls specifically, the correlation is hard to ignore: reps who talk less and listen more uncover more, and they close more.
The reason is not the number itself, it is what a low talk ratio means. A rep doing most of the listening is asking real questions and following the buyer's lead instead of pitching past objections. A rep talking seventy percent of a discovery call is usually presenting to someone who has not been qualified yet.
Coach it as a symptom, not a target. Pull the calls where the rep talked too much, listen to where the conversation went one-directional, and work on the questions that were not asked. Chase the behavior and the ratio follows. Chase the ratio alone and you get reps who go quiet without getting curious.