What does it mean, 'inner' and 'outer' (popup)
Water below Mountain: the world is tough like a mountain, you need all your wits to live in it and often just to survive. Water makes you eager to learn, and it comes easy. But it also means you don't know much yet.
Water has no form, but it can fit in things, adapt, learn, absorb. It can also mean you think you're the tough one while having nothing solid inside yet, and then you're just dumb.
Ideogram of the hexagram name: the upper part is weeds and a cover, the lower part a pig. The weed is probably Dodder, which covers everything, putting it in the dark. The pig underneath cannot see anything.
The 'Great Image' says: At the foot of the mountain a spring wells up: Ignorance. A noble one nurtures virtue by reliable conduct.
Hex.4 is the contrast of 49, turning things over because you know how to improve them.
Hex.4 doesn't know much, but wants (or has) to learn. The hexagram talks about both, the teacher and the pupil. A good teacher learns as well.
One has to care for the ignorant, the formless. It still has unlimited possibilities. Without it, life would die away by lack of renewal.
Blessed are those who have something of this in their mind, how little it may be.
And listen carefully to those who speak from out this unborn thing. They are the true sages. Lao-Tze said: “I am ignorant, like a baby that has never yet laughed ...the people are bright, bright, I alone am dumb, dumb”. (DaoDeJing verse 20).