At the airport, never get in line behind anyone with children.
At a European airport, never get in line behind anyone carrying sticks (some weird thing for folks coming in from Africa)...same rule above applies for children.
At any airport bathroom, never touch anything but yourself. Ever. Even if it means not flushing or washing.
In France always say "Bonjour" before engaging in any conversation or attempted conversation. (had a cop berate me for asking directions without saying that first)
After all your calculations, discussions, sweat, tears and consternations, 4% is about what you can withdraw safely.
Leave your hotel room key where you can find it in the dark and even in an emergency never leave the room without it. Keep your room safe unlocked the night before you leave.
When dealing with your local marina, ALWAYS ask "how much will this cost" first.
The 80/20 rule applies to almost everything. If a concept/plan/idea works 80% of the time, that's usually good enough to get through life.
The best weapon in the world is the first thing you can grab.