I biked for many years in Boston, MA, and the advice to assume that everyone is out to kill you rings true. I've ridden along and between cars, trucks and buses always assuming they can't see me, and never had any accidents. However, what got me multiple times over time is doors opening suddenly on stopped cars (the last time on a car in a traffic lane idling at a red light, opened by an exiting passenger). So if you're riding in those conditions I think you should assume they are out to get you by suddenly opening doors :-)

It puts a big damper on bike commuting because it means you need to move very slowly along rows of parked cars, as well as stopped traffic.