Is knowledge possible? Strictly speaking, we don't know -- this concept is known as Cartesian doubt. However, we should assume that we can know things. Specifically, we should assume that our Reality and everything in it can be understood as a deterministic machine -- understood by visualizing a model of how it works.
A beautiful verse in the opening of John's Gospel might well be describing this concept:
All things were made through it [the Logos]; and without it was not any thing made that was made.
The Logos in this context would refer to the plan, to the design of the reality-as-a-machine. This Greek word might also refer to its simulation -- a simulation that we, humans, visualize in order to understand how this machine works. This Logos -- this simulation -- is knowledge.1
And while, again, this is only an assumption -- that we can know things -- there are rational reasons why we should assume just that. The main reason is that knowledge is useful. That's why we have evolved this capacity -- to know, to understand -- in the first place. It gave our ancestors a tremendous evolutionary advantage, it lifted them to the top of the food chain "and let them have dominion over the fish of the sea, and over the fowl of the air, and over the cattle, and over all the earth, and over every creeping thing that creepeth upon the earth." (Genesis 1:26)
In other words, humans would not exist if this assumption didn't hold true.2
Why we doubt it then? Well, there are a few reasons. Socrates uttered his famous words, "For I was conscious that I knew practically nothing..." during his trial by the jury of 501 citizens of Athens, the trial that ended in his death sentence. We want to believe that we are rational individuals living in a rational, predictable world. The truth is that we are not -- not when it comes to human interactions -- because while knowledge is possible, it is also optional. It is also hard to obtain -- it's hard to piece together one's understanding, one's map of the Reality. And the hardest part is to start.3
It's not unusual for a person to have very little of the map completed. But even when we think we figured out a few things about this world, a day may come when the life forces us to question even a most deeply held belief. And when that happens, it makes us feel as if we know nothing at all. We walk the same streets, we see the same people, but it feels like we just landed on a different planet.
Verily I say unto thee, Except a man be born again, he cannot see the kingdom of God. (John 3:3)
1 You can also think about it as a map of the Reality -- we need knowledge to find our way around. Without it we are walking in the blind.
2 Which also makes it a scientific theory in its own right.
3 And because no matter how knowledgeable a person is, their choices are still intuitive -- and human intuition is only partly based on knowledge. Rather, it is based on the lifetime of experience, the knowledge being only a part of it (if even).