Newton's first law of physics states that there is an inertial quality to bodies: those in motion tend to remain so, while those at rest do so too, unless there are external forces. Is it possible that humans exhibit some version of this? Habits are one example, with bad ones being hard to stop and good ones hard to start (at least for me). Researchers have recently shown that there is a shopping momentum effect too, whereby a consumer can't help buying more once an initial purchase has been made. This does not relate to consolidated buying (saving time by buying many items on one trip) or complementary buying (going in to buy a suit and buying shirts and ties to match). Shopping momentum is when an initial purchase (driver product) triggers additional purchases (target items) that otherwise would not have been made.