Thinking that you have pretty profound UNIX knowledge? Think again if you don't know how to
This introduction to strace by Chad Fowler finally persuaded me to check out this little UNIX tool. I made several attempts in the past, but each time I attached it to a running process, I just saw, well, gibberish. And as no one else on my teams in the last years was fluent with strace, I kind of gave it up each time. But by reading that post, I learned that this gibberish is not that hard to read after all. In fact, it's pretty much straight forward and contains so much useful information that is hard to obtain otherwise. I can only guess how many times this knowledge would have helped me in the past.
Related: Introduction to lsof, a great companion to strace.