from Kyabje Gelek Rimpoche's extended commentary on the Lama Chöpa:
Remember, there are three problems that can happen when you listen to teachings. The example for the first problem is when the pot is filled up and you can’t pour anything else in. You can see it in the Chinese movies when a tea cup is full and they keep on pouring until all the tea overflows. If you have prefabricated ideas, it means your cup is already full. You expect to hear certain things and when you hear them, you like it, and when you don’t hear them, you are disappointed. If you come with that state of mind, you don’t have an open mind. Your cup is full; there is no room for anything to go in.
The second problem is when the pot has a hole. Either you just sit there and don’t even listen or you may listen, but it goes in through the right ear and out through the left. You may write things down into your notebook or record them on your tape-recorder, but then never read the notes and never listen to the tape-recorder. That is the hole. There is no use in that.
Another problem is when the pot is dirty. When your cup is dirty, you cannot drink from it or use it. Even if you put lion’s milk in it, you cannot drink it. That is the traditional example. It is toxic. Toxic here refers to spiritual toxins, things which harm us. What are these? They are doubt, disrespect, just pure curiosity and inquisitiveness, and looking only for faults. These are the real toxins. If you are only looking for faults you don’t even have to sit here. You can find faults anywhere. If you are doubtful and suspicious, better not waste your time; it is not going to get you anywhere. You have to be intelligent and sharp-minded. You have to ask questions, but you should not have doubts in the sense of wondering whether it is really true that there is something called karma and is it really true that there is a Dharma, and so on.