The Socratic / dialectical phrase:
I know one thing: that I know nothing.
If one were to subvert it to
- I know one thing: that I will know nothing.
Is it a maxim that can guide practice, in any conceivable way?
"A fool who knows his foolishness is wise at least to that extent, but a fool who thinks himself wise is a fool indeed." - Dhammapada 63
If a foolish person were to become aware that he is foolish, there is potential for spiritual growth. But the fool who thinks that he is wise, blocks himself from any spiritual development due to his delusion.
Not quite sure what you're looking for. The I will know nothing has positive effects in the sense that it will allow us to lead life in a more common sense fashion. It also jogs our spiritual side in the sense that we observe ourselves and our surroundings more. We tend to quieten ourselves a bit more and be more humble with regard to the vast expanse that is the universe and us being the tiniest of tiny specks in it. We get back to the basics.
When we realize we don't know something we automatically start asking questions about it. To try to know what we don't know is in our nature. We are curious. A background process starts running in our mind questioning existence and everything in it. This aids our practice. Or rather our life becomes some sort of practice in itself. We tend to just feel this moment a bit more.
There are two benefits of recognizing self-ignorance: low-level and high-level.
The high-level is the recognition of one's fundamental ignorance. This is crucial for the Buddhist process because this is the very first step in the Buddhist process-of-becoming-who-we-are, the chain of causation and understanding that piece of philosophy. Read more about it for more info.
The low-level version is recognizing one's conventional/relative ignorance. This low-level version actually has the most practical benefit!
Here, this understanding of our relative ignorance has the benefit of being more compassionate towards others (as well all the other Brahmaviharas in some way), developing eagerness to learn the Dharma, being more open to new knowledge, being more aware of one's own mind and transgressions, and just overall being a good person because you know that you don't know so might as well do good!
I know one thing: that I will know nothing.
Even at "ultimate-level", it is mostly true because as the Diamond Sutra states, the person who is Enlightened, does not know of a person who is Enlightened. There is no ego, individuality, or a person, furthermore as the Heart Sutra says, there is no suffering, no cause of suffering, no knowledge, nothing. These were all illusions piled on top of illusions for the sake of leaving illusion..
This is agnosticism, a view that the Buddha explicitly calls stupid in the Brahmajala Sutta. I quote from my book, Conversations with the Buddha, p. 22 (see also p. 25):
"The ‘Eel Wrigglers’ (amaravikkheppika), which can also be translated as ‘endless equivocators,’ are agnostics who refuse to commit themselves to any view, but simply say, “I don’t say this, I don’t say that. I don’t say it is otherwise, I don’t say it is not. I don’t not say it is not.” This belief, if we can call it that, is based on the desire to avoid lying, attachment, and cross-examination, which comes simply from not knowing. These are the first three arguments. The fourth argument is because one is dull and stupid."
This view should be distinguished from the view that the dharma is trans-linquistic and trans-rational, although the two views are often conflated, especially by Western students.