The first few weeks of the NFL season are tough to gauge in the fantasy world.
Teams aren't putting together a true game plan in the preseason, so it's hard to put too much stock into production. The preseason might feature some impressive individual performances, but it's much different when first-team offenses face first-team defenses for an entire game.
While it's simple to start your studs, you'd be ignoring obvious tough matchups. You might think twice about using Alfred Morris and/or Matt Breida with the San Francisco 49ers facing a stout Minnesota Vikings defense.