Why is Knowledge Important?
Knowledge is, roughly, useful information. It is information that's adapted to a purpose. It is good explanations, and it is solutions to problems people had. Knowledge shouldn't be expected to be perfect. A partial solution is still knowledge, even if it contains some mistakes, and can be improved on in the future.
Knowledge is created by imaginative and critical thought. The key ingredients are both creativity and criticism. We need numerous ideas, including ones that aren't obvious. And we need error correction to get rid of flaws. With those two components, we can improve our knowledge and learn new things.
It's also important to be sensitive to problems. Problems are opportunities to learn something new, and to improve our lives. But some people are scared of problems, or consider problems inevitable and permanent. "Life isn't perfect, and who do you think you are trying to do better than thousands of smart people before you? Some problems are never going to go away, and you should just get accustomed to them." These people don't notice, keep track of, and make an effort to solve problems as well as they could with a better attitude. That means they solve fewer problems, and correct fewer of the problem-causing flaws in their ideas.
Problems can be solved and knowledge can be created. What is there to stop us? There are the laws of physics. We can never make a perpetual motion machine. And there's our preferences. If we don't want to solve a problem, we won't. And there's our knowledge. If we don't know enough about a problem then we may have to learn more before we solve it.
None of these obstacles should ever make us unhappy. It's possible to have a great life without violating the laws of physics. It's possible to have a productive, happy life without knowing everything: just work on accessible problems and make progress. If we want to live in this way, we won't be upset when we don't solve some other irrelevant problem.
Most people think that knowledge is justified, true belief. This is an authoritarian conception of knowledge, and a perfectionist conception. It insists that if an idea is only a partial solution, or contains a mistake, then it's not genuine knowledge. And it encourages appeals to authority which serve as justifications.
If a person believes that he has a justified, true belief then he has no reason to listen to criticism of his belief, or to listen to dissenting opinions. Any idea which contradicts a true belief must be false. Therefore, all criticism is irrelevant, and anyone who disagrees is mistaken. The only thing to do is educate them, not debate with them, and not consider that they might be right and we might be able to mutually learn from each other. Confidence that one definitely knows the final truth leaves one with no reason to try to correct errors; it's actually foolish.
Justification is a chimera. Suppose I justify an idea with a justification J1. Now let's consider J1. J1 is itself an idea. And it might be mistaken, so we'll need to justify J1 too. So we do: we think of a justification of J1 which we'll call J2. Unfortunately, this leads to the same problem again. How do we know J2 is correct? So we offer J3, and then J4, and so on. And every single justification is critically important. If J3 isn't correct or isn't justified, then neither is J2. And if J2 isn't, then J1 isn't justified. And that would mean the original idea isn't either, which would mean it's not knowledge according to the justified, true belief conception of knowledge.
As you can see, justification leads to an infinite regress. There is no end to the justifications needed. There are two ways to try to get out of this problem. The first is circular. You use J2 to justify J4, say. But circular arguments are invalid. The second way out is to declare some ideas to be self-evident or self-justifying. When you get to them, you just stop, and you never consider if they might be mistaken. This is circular too. It's justifying J4 using J4. Further, how do you decide which propositions are self-justifying? You'll need an idea about that, and it needs to be correct, so you better justify it. No problem has been solved.
The way out of this mess is to stop seeking justifications at all. Instead, we can pursue knowledge as I describe it above: imperfect but useful ideas, which we don't claim are justified, but we do improve as much as we can, and remove as many errors as we can from. In this way, our knowledge is our best ideas so far. What's wrong with that?
A common question is if we don't accept justifications, then how can we ever take practical action when we don't have a justified, true belief about which action is best. This is easy. We should act on our best ideas. What else would we do? Act on ideas we consider inferior?
Using the justificationist approach, when we consider a new idea the main question asked is, "How do we know this is true? How can we support or prove it?" Support and proof are just different words for "justify", and have the same problems I described.
When we consider a new idea, the main question should be: "Do you (or anyone else) see anything wrong with it? And do you (or anyone else) have a better idea?" If the answers are 'no' and 'no' then we can accept it as our best idea for now.