Most teams select a player in the first round with the hopes that he becomes an immediate starter. However, there are plenty of players that don't fulfill those hopes. The reasons vary from things like having a veteran ahead of them on the depth chart or the player needing more time to develop.
Even if a rookie doesn't have a chance to start early in his career, it doesn't mean he can't make an impact. According to Pro-Football Reference, Aldon Smith didn't start a single game for the San Francisco 49ers but still registered 14 sacks.
Please keep in mind that these odds don't account for injury. Of course, an injury has the potential to elevate any of these players.