So we need to hear feedback. So far so good. But what to do to hear those who don't talk to us? Whose do not fill out feedback forms, don't reply to mails, do

So we need to hear feedback. So far so good. But what to do to hear those who don't talk to us? Whose do not fill out feedback forms, don't reply to mails, don't talk on the phone? They don't care enough to respond. They don't know how to respond. But at least some of their insights are valuable. How to reach them?