Exactly, although Roman is not trigger happy like 5-6 years ago, any Chelsea manager knows he must deliver something in the first season, or else.. Let's say we drop a couple of games in December and back in the dog fight for the 4th spot, suddenly everything Sarri has done so far will be forgotten and he's under pressure. With that much pressure, any manager would go for the high percentage play of playing/buying the proven player, instead of betting his job on a 20 year old from the reserve team. This is not Liverpool or Spurs, Klopp/Poch get 3-4 years of building a team with no expectation of winning anything, of course they could take a few more chances with youth players.