People who come and ask for teaching, but their cup is full; you can’t put anything in.
Before someone can teach, you’ll have to empty your cup.
This is harder than you might realize. By the time we reach adulthood we are so full of, um, stuff that we don't even notice it's there. We might consider ourselves to be open minded, but in fact everything we learn is filtered through many assumptions and then classified to fit into the knowledge we already possess.
The Buddha taught that conceptual thinking is a function of the Third Skandha. This skandha is called Samjna in Sanskrit, which means "knowledge that links together." Unconsciously, we "learn" something new by first linking it to something we already know. Most of the time, this is useful; it helps us navigate through the phenomenal world.
But sometimes this system fails. What if the new thing is utterly unrelated to anything you already know? What usually happens is misunderstanding. We see this when westerners, including scholars, try to understand Buddhism by stuffing it into some western conceptual box. That creates a lot of conceptual distortion; people end up with a version of Buddhism in their heads that is unrecognizable to most Buddhists. And the whole is Buddhism philosophy or religion? argument is being perpetrated by people who can't think outside the box.
To one extent or another most of us go about demanding that reality conform to our ideas, rather than the other way around. Mindfulness practice is an excellent way to stop doing that, or at least learn to recognize that's what we're doing, which is a start.