I would say the 'belief' a player will improved isn't just a prayer, it's based on research and watching a player practice and play in games and understanding what his weaknesses are. Based on what they see and their combined decades of coaching and evaluation experience they determine that a player should improve after his rookie season enough to warrant not using another high draft choice on the same position the next season. I'm sure they have a plan B or C or D, (backups, FA's, trades...), but obviously those choices aren't as good as Plan A. I think you either don't understand how teams plan their roster or just look to criticize. It's not bad to not understand, none of us really do, but most , I think , have a better understanding than you do.