The kind of listening we're trained to do in school and at work is passive listening. Sit still. Get through it. Figure out what's going to be on the test and ignore the rest. Your eyes can glaze over, but don't let it show. Try not to nod off. People are talking, and they'd like the illusion of listening to accompany that. Don't interrupt.
Passive listening is letting the other person talk.
Active listening, on the other hand, requires that you interrupt when you need a clarification, and it requires that you ask a truly difficult question when the speaker is finished.
If it's worth listening to, it's worth questioning until you understand it.