Complexity and how it accumulates

the rules really are that fiddly, because tax law is that fiddly, and no rewrite will make them simpler.

Essential complexity

half the file is there to work around a framework decision that has nothing to do with the feature.

Accidental complexity

you asked where the pricing logic lives and were told it depends which of five places you mean.

Big ball of mud

one class is four thousand lines and every feature branch touches it.

God object

nothing is broken, but the way the parameters keep getting passed through five functions feels wrong.

Code smell

there is a dead flag, three commented-out blocks and a helper nobody has called since 2022.

Cruft

you built the plugin system for the second provider, and two years later there is still only one provider.

YAGNI

there is an interface, a factory and a strategy, and exactly one implementation of each.

Speculative generality

you copied the block a second time and left it alone, and only pulled it out on the third.

Rule of three

the VAT rate changed and you had to find it in eleven places, and missed one.

Don't repeat yourself

two functions looked identical, you merged them, and a month later you added a boolean flag to tell them apart.

Incidental duplication

you hand-rolled a cache for a function that turned out to run twice a day.

Premature optimisation

the design handles ten thousand requests a second and the product has forty users.

Over-engineering

the ticket was done on Tuesday and you spent Thursday adding polish nobody asked for.

Gold plating

the rewrite is going to fix every compromise in version one, all at once, and it is nine months late.

Second-system effect

the answer was Kafka again, and the problem this time was a nightly report over four thousand rows.

Golden hammer

you went in to fix one bug and renamed the two variables that made the bug hard to see.

Boy scout rule

the first person skipped the test, and within a month nobody in the directory was writing them.

Broken window theory