Pochettino looks like he will fail to build a new era for Chelsea, he only marked its revival with transfer market movements, not with match results. If we wait longer, I'm not sure Pochettino will last more than two seasons at Chelsea. It could be that if the Blues suffer another defeat in the EPL, then he will leave sooner before seeing the players he recruits develop well.
I think if Chelsea loses to a club like Liverpool or Man City it still makes sense, because they are fellow big clubs. However, losing to Nottingham Forest clearly disappointed all fans, I think.
You don't realize that Chelsea is starting from scratch and that Pochettino needed time to mold the Chelsea players into the squad he wants them to be. None of the new players Chelsea added to their roster have mastered the art of playing in comfortable possession to win games and to prove their abilities in a match (how excellent they are), some recently signed players haven't even appeared in a single match since they were signed.
Instead of criticizing Pochettino for how far he can take the Chelsea team, Chelsea fans should show him patience and support.