Everything written down is probably unimportant

Knowledge, knowledge, knowledge. If knowledge were power, books would be smarter than people. It's careless to stress the importance of facts without admitting that facts are only as useful as they're understood and used by people.

There are two ways to learn.

First is to memorise everything. That's like taking a function and caching all input/output pairs so that the function is fast. This happens when people are motivated only with how quickly they get answers.

Second is to focus less on the input/output, and more on making the function itself better with time. So rather than memorising facts, you learn to think about facts differently. Given the same inputs, you keep getting better outputs.

When you look at the world from the second perspective, everything written down becomes data with a short shelf-life. What matters is how you interpret them.

For example, it's important to understand the concepts of programming so that you can easily learn new things as the world changes, rather than memorising afresh anything new that comes in. This is why experienced engineers don't emphasise remembering things that can be looked up.