It is a mistake to think that you understand anything completely. Something is always missing.
I’m not the first to point this out. In 1233, Zen master Eihei Dōgen (source) wrote:
For example, when you sail out in a boat to the midst of an ocean where no land is in sight, and view the four directions, the ocean looks circular, and does not look any other way. But the ocean is neither round nor square; its features are infinite in variety. It is like a palace. It is like a jewel. It only looks circular as far as you can see at that time. All things are like this.
Right. Everything apprehended by the mind, everything perceived or conceived, is more complicated than it seems. Actual things (objects, events, situations, states, whatever) have vast numbers of details that are not represented by the mind. Moreover, actual things are actually related to other things in vast, perhaps infinite, numbers of ways.
It is like a palace. It is like a jewel.
The ocean is also like water sloshing in a tub, like the hydrocarbon lakes of Titan, like human blood. While the ocean is a great example, vast numbers of things are true about anything, beyond the capacity of any finite set of minds to perceive, or to grasp.
Dōgen goes on:
Though there are many features in the dusty world and the world beyond conditions, you see and understand only what your eye of practice can reach. In order to learn the nature of the myriad things, you must know that although they may look round or square, the other features of oceans and mountains are infinite in variety; whole worlds are there. It is so not only around you, but also directly beneath your feet, or in a drop of water.
Thus, it’s not that there is no reality, or that no true understanding of reality is possible, it’s that understanding is always incomplete. This is so because we are limited in our powers of perception and conception, and because reality is very complicated and interconnected.