The Worldwide Web is very useful for finding out many things. Unfortunately, this can lead to one being rather ignorant in some ways.
The first way is that if you can look it up, why bother learning it? The answer to that is that having the information readily available to think with, one can think with it easily.
For the same reason, I find knowing basic arithmetic very useful. I can often estimate an answer (and sometimes figure the exact answer) before someone has fished out his calculator (or other device with a calculator) and started entering the problem.
Which of us do you think uses arithmetic more often?
The second way is that one can have a bunch of links to information and not keep track of them.
I recently had a problem with my browser and had to clear my browsing history and restart my browser. I lost several links and have been unable to find them with a Web search. If it had not been so easy to just keep them open, this would not have happened.
The third way is that even if you do learn the material, you are all too likely to just get the gist of it, because you can always look it up later.
This is similar to the first reason, but has the added point that you might really think you know the material. Should you have to apply the material, you may find that your understanding is not what you thought it was. Or you might not find that out. Either way could result in a disaster.
The Web is very useful, but do not let it stop you from thinking.