I tried to explain this just yesterday to a colleague who complains about my long emails. He said this obviously demonstrated I had no logic in my brain. It was an annoying day.

Writing a short email is easy. All it takes is actually knowing what you're trying to say.

IMHO, this is simply not true.

Practice makes perfect. Writing short, concise pieces of text that express your thoughts in an easily digestable is really hard, a challenge of its own (despite what you want to say) - it's like a form of "professional" art, that few master.