Imagine that you go out on the lake with your speedboat, or you take to the seas with your boat. It's a sunny, beautiful day -- but a bit windy. While you're out there, you enjoy a beer or two. This isn't out of the ordinary in many boating trips for many people, but on this day, the influence the alcohol has over you feels stronger than ever before.
Eventually you are "pulled over" by the authorities and accused of boating under the influence. You try to explain that your seemingly erratic boating was caused by a number of factors, but the authorities don't want to hear it.