1.8L with a 3 qt sump has each quart holding down .6 liters. My M54 BMW engine had 6qts covering 3.0 liters for 15k miles according to their insanity. That's .5 liter covered by every quart. Not too far off the mark really....
3 quarts of oil has to make a lot more trips around the engine than 5 quarts does. Every time that oil molecule has to make a trip, he's getting battered by engine parts. He's literally getting the life squeezed out of him. He wishes he could just stay in the sump and relax.