Sitting on the plane, waiting for the beverage cart, I was pretty thirsty so I asked the flight attendant for the rest of the bottle (about 3x the water in a cup). She gave it to me, no questions asked.
A half hour earlier, two gentlemen asked to cut me in the security line because they were late for their flight. They asked politely and directly so I said, of course. Nobody behind me complained. They cut probably 10 minutes off their wait time—maybe the difference in making their flight.
At dinner a couple nights before, the waiter sat my girlfriend and I at the bar near the entrance at one of my favorite sushi spots in SF. I asked her if it would be possible to get a table for two in the back nearer the music. We had to wait five extra minutes but we got the table.
Physical laws are set, seemingly. You cannot negotiate with gravity about jumping out of the plane and you cannot negotiate with sushi to taste differently (not including soy sauce).
However, you can ask people to break the rules that are set by somebody else and stay that way just because everyone agrees to play along.
Not everyone can do this at the same time. And no one person should do it all the time. But you should remember to do this when you need/want something that only a social rule would keep you from getting.