We all go through programming disasters. It's hard, if not impossible, to always make the right decisions. And after we've steered the ship back on course and we're out of the storm, we try to review if there was any way we could have prevented the storm in the first place. This reflection is crucial, and is one of the best ways we can improve ourselves.
What becomes dangerous however, is when these reviews turn into policies, or mandates. To explain why, I'll summarize an anecdote which I've come across from the Extreme Programming book.
A mother was baking a ham with her daughter, and she noticed that the ends were cut off. She asked her mother why, to which the mom responded: "I don't know. That's the way my mother always did it. I'll ask her." So the mother asked the grandmother why the ends of the ham were cut off, and she said: "I don't know. That's the way my mother always did it. I'll ask my mother". And the great grandmother's response was: "My oven was too small, so I had to cut off the ends to have it fit".
Blindly following policies can lead to extra steps that can work against us. Rather than come up with new policies, it's better to come up with principles that can inform future decisions. It's more important to understand the reasons behind what those policies would have been.
On that note, dogma itself is dangerous. When we start blindly following rules, we start becoming simple machines. It tends to stifle creativity, which is the worst thing that can happen to programmers. Programming itself, after all, is a creative process.
I've seen a trend by programmers to be completely against any form of duplication. After all, there are extremely compelling motivations for this idea. Programmers have all copy/pasted code to get something working, with the reason being that it usually ends up working much faster in the short term. But then when all that new code needs to get updated, we've all forgotten to make the change to all the pieces that required it. And bingo, we have a new bug.
Then we look back on it and what's to blame? Not that we forgot to make the change everywhere, which was just the symptom. The problem was that it was possible to change one of the parts, and forget to update the other. It should have been refactored to avoid the duplication, so that a change in one location would naturally affect all the other paths. This would have prevented the bug from even being possible.
But like most dogmas taken too far, this can get you into trouble. Here's a very contrived example, and granted most of us don't think this way, but I've experienced somewhat similar arguments for avoiding duplication where I thought it was just silly.
a = 7
b = 3 + 12
c = 18 - 2
d = 9 * 6
Try to pretend that these are real calculations, and there are not just hardcoded numbers here. Can you spot the duplication? Normally you'd say there isn't, but I can argue that there is. You have four assignments, and 3 mathematical operations. Isn't that duplication? Here's the "reduced" version:
vars = ['a', 'b', 'c', 'd']
arguments = [(), (3, 12), (18, 2), (9, 6)]
ops = [lambda *x:7, operator.add, operator.sub, operator.mul]
for var, args, op in zip(vars, arguments, ops):
globals()[var] = op(*args)
Notice how I've eliminated all the duplication? And wasn't it clever of me to fit the simple assignment in the first example to a no-op? The logic is all now in a single line compared to the 4 up above. I can argue that although it's actually more lines of code, I can effectively move all but the loop into configuration. Now people can add more variables to the global namespace, with an arbitrary operation performed on any number of arguments, all through configuration! What a wonderful and extensive system I've created!
The perceptive reader will have discovered that I was being a tad bit sarcastic. (My co-workers will all tell you that I'm subtle). So which is easier to understand? Which would you rather maintain? Readers with no python experience will probably understand the first code snippet. But you probably need to know python to even attempt to understand what's going on in the second.
So if you're going to follow dogmas, policies, or rules, then follow this one:
Always use your brain.