That doesn’t mean feature paid itself off if you invest with idea that it will be useful for more than 1/5 of users and when feature brings single customer an

That doesn’t mean feature paid itself off if you invest with idea that it will be useful for more than 1/5 of users and when feature brings single customer and is marginally useful for other customers. Then also you have ongoing costs of maintaining the feature that no one usually accounts for. Even if customer participated financially into creating the feature when they leave you are left with maintenance.