My favorite Ron Jeffries quote, from the NeverIsNeverNever page on the C2 wiki:

I know that if you agree NEVER to let the unit tests drop below 100%, you'll only do it that one time when you just couldn't figure out an incremental way to change all the deductions from negative to positive. If you agree NEVER to keep a task open for two weeks, you have a better chance of finding the way to do it incrementally, and that one time you'll make sure you've sucked every idea out of the universe before giving in.

When I say something should never be done, it should mean that you'll never do it unless you really have to.

And if you really have to, you'll ask everyone you know first so you still won't have to.

And if you still have to, you'll be looking over your shoulder scared to death that I'm going to materialize there and say "why didn't you just ..." and be RIGHT, and EVERYONE will know you're an idiot.

When you're sure that you'll be able to say "because X" and I'll quietly lower my eyes and say "oh" and de-rez back to wherever I come from ... then break the rule.

Then do one more thing. When it's over, and you've suffered - as you will - for breaking the rule, think back and figure out what you could have done, and learn the deeper meaning of NEVER.

Thunderstruck by AC/DC seems to be one of the more popular cover songs that bands perform. Here we have the fine fellows from Steve'n'Seagulls, a Finnish Bluegrass band, performing a rousing rendition of Thunderstruck.

The fine fellows of 2Cellos not only play well, but they have great videos for some of their cover songs. Here they perform Thunderstruck by AC/DC.

(One from the archives. Not sure when I wrote this. I think it still stands.)

These days, with the rise in programmer testing (also known as unit testing to its friends) much testing effort is put into ensuring that program logic is correct. This is good and to be encouraged at all times. A program that does the right thing is always more likely to be correct than one that does not. Interestingly, with all of this new-found enthusiasm for testing, there seems to be a few gaps in our approach. The one I'd like to discuss here is the principle of "Always Valid".

This principle is easy to arrive at from first principles. You see, programs do stuff. Every programmer knows this. We know it because we're the ones that tell them how to do it. But pause a moment and consider what this "stuff" is most of the time. The vast majority of the time we're processing data; and it's the data that is the star of the show. Our programs are just descriptions of what we want to do to that data. The data is the important thing.

I love eccentric cover songs and what better way to start a series of these than with Enter Sandman by Metallica played on a banjo?