The beauty of daily fantasy football is that, unlike a season-long draft where someone is tied to their top players all year, any top players in the NFL can make their way into your lineup. While that can be a blessing, it can also be a curse.
Although you're able to roster Christian McCaffrey, Dalvin Cook, and Derrick Henry all at once if you want, it is unlikely that all three running backs are optimal plays at their respective salaries for a particular week. There are many elements to decide which players are the best plays, and a large aspect of daily fantasy is the matchup a player has.