Jeff Atwood's blog entry "Please Don't Learn to Code" has triggered a huge number of responses. Among the better ones was Michael Lopp's "Please Learn to Write" and Scott Hanselman's "Please Learn to Think about Abstractions."
Reading Hanselman's entry I noticed that he made an implicit point that is key to thinking and reminded me of one of my favorite things about Art Markman's book Smart Thinking, which I recently reviewed. He has an entire chapter about the power of self-explanation for enriching knowledge.
In this case, Hanselman's wife actually had no knowledge of plumbing—she just knew about operating the faucet. But I'll bet that she would have said she knew something. Markman recommends that you challenge yourself to explain any knowledge you presume to have. In doing so (and using some of the techniques he offers in the book), you'll quickly realize that there are gaps in that knowledge.
Once you know of the gaps, you can easily fill them in. In the beginning, your knowledge feels sufficient even though it has holes. After a short burst of self-explanation and accompanying research, you'll feel much more confident.
You shouldn't tolerate complacency in any area of your life and the best way to accomplish that is to become an active thinker.