Exactly. Baseball is that one sport that depends so heavily on what players, especially hitters and pitchers--and that's just about everybody--do as individuals. Porcello gets the ball at the beginning of the game, and it's almost entirely on him. The defense can help--and did last night. The catcher last night was our best defensive catcher, Leon. The only weapon Farrell had left was the bullpen, but those 6 Astro runs in the first three innings and the paucity of Sox hitting took that weapon away.
What I'm reading says that everybody knows what Porcello's problem is. He is keeping every pitch up in the strike zone. The pitching coach is reportedly working with him, but so far to no avail. He still has the same repertoire that worked so well last year, but lacks command, and we have seen enough pitchers like that to know it can be disastrous--see some outings this year by Pomeranz and Price.
The manager is equally helpless when a hitter goes into a slump, for which remedies include days off, extra batting practice, more attention from the hitting coach--none of which will work until the hitter somehow finds his swing again. This year see Beni, JBJ,and others, but especially Pablo.
The nature of MLB today is such that every single swing by a hitter and pitch by a pitcher is recorded and scrutinized to the nth degree. Hell, espn, fox, and other networks can do some of that analysis themselves--and do, with stop-action video to make the point stronger.
To me the manager has one really good weapon at his disposal, his bullpen, and even the bullpen depends heavily on individual performance over which the manager and pitching coach can have only a small effect.
He also probably needs to keep his players in the right frame of mind. I'm guessing here, but I think relaxed and very focused on what's happening are about right. I think the Cubs manager probably does that well and this definitely helped last year when they won it all and broke an incredibly long no world series streak. But guess what? This year so far that exact same team has a losing record to date, so what the hell do I know?