If there is a line, or even a character that you can remove and still show the problem you have too much code.
Oh, yeah, sure. Golfing examples to show the unwanted behaviour!
I seriously advice to not follow this advice to the letter. Else, you'll remove from your example an easy 2 lines and 25 characters, and are pelted by remarks you should use 'strict' and 'warnings'! Or in an effort to remove characters, you reduce your example to use single letter variables (without using my!) - and instead of people spotting your error, you'll get a ton of replies to use better variable names.
Writing a short example is good - but don't golf. The example should be clear: it should only do what causes the problem, and it should be optimized for the reader. Which isn't the same as "write it in as little lines and characters as possible".