“Sometimes what goes without saying is best said anyway.”
– Iain M. Banks, The Hydrogen Sonata
One of the most common mistakes that I see other people do, and my self quite often as well: It is to end a meeting or a conversation without summing up what was decided upon. It might seem perfectly obvious to you, and it probably is perfectly obvious to all the other people there. The problem is that in many cases what is perfectly obvious might not be the same thing for everyone there.