There's a great line from Robert Frost's poem "The Road Not Taken" that I've always thought applied to software engineering and software testing. The line from the poem is: "Two roads diverged in a wood, and I took the one less traveled by, And that has made all the difference."
Sometimes however, the road not taken is not taken for a very good reason! It can be the case that this road can lead down a rathole and is based on bad software design, poor implementation, or tactical mistakes.
As a similar construct to the fundamentals (the "rules") of software testing that I first mentioned in an earlier post, I'm also going to start a series of periodic posts on mistakes that people often make. In other words, the ratholes into which we all fall when we choose the wrong road.