Rule 1: Your trousers should fall so that there is one clean break at the front, and none at the back.
Rules are there for a reason, but there is nothing wrong with breaking them. These statements are not contradictory. That is one of the most important things to understand about the traditions of menswear.
All rules are there for a reason. They are useful rules of thumb that become formalised over time. And they become formalised because they have practical advantages that encourage men to apply them regularly.
So why is the generally recommended length for men’s trousers? Because it creates a clean line at the back of the trouser, adding to the lengthening silhouette that is the suit’s main aesthetic advantage. Because when a man is walking it looks more elegant if his suit trousers flap less and expose less of his ankle.
If the trouser were longer, it would create a puddle of folds that could ruin the silhouette of a suit, dragging the eye down and making a man look shorter. If the trouser were shorter, it would flap around the ankle and remove any elegance – probably reminding the viewer of a schoolboy in short pants.
That’s why the rule, or guideline, exists. But once you know this, there is nothing wrong with breaking it. Knowing why the rule is there helps you break it well.
For example, men on the European continent tend to wear their trousers shorter than is recommended here. They do that because they wish to expose their footwear, and perhaps their socks, to more inspection. Both are more a part of their outfit than for a English or American man. To quote one famous Italian “I don’t necessarily want people to see my socks, but I want to make sure they can see my shoes.”
Now, if men on the continent simply wore their trousers shorter, they would encounter the aforementioned problem with flapping. But they aware of the rules and why they exist. So they wear their trousers narrower as well, fitting them closer to the ankle and minimising any flapping. Hey presto: the shoe is on display, the silhouette is intact, but it is still possible to walk with elegance.
Once you know why the rules are there, you can work out how to break them effectively.