Yogi: I notice that greed causes the mind to suffer.

Sayadaw: You want something, you want to grasp it and the mind is tense; it makes the mind suffer.

How do you know that it is greed? Because you already know the characteristics/nature of greed, that’s why you can say that there is greed.

But if you understand that greed is suffering; why then is greed still so strong?

If you still have a lot of greed, it means that the understanding is still not enough; the mind needs to learn more.