The player is of course the only one who has real agency in the game and the game and it's characters react to the player's actions, so you can look up guides to plan out your companions' reactions. Taken to the extreme, you can save-scum, reload or use mods to alter the world to your liking.

This here is more about that the other companions have an opinion on how their story is supposed to play out, a set path which they favour unless your interactions with them sway them from it or confirm their believes. For example you can get an accidental God-Gale/ Dead Gale if you did not notice that you pushed him too much towards ambition or didn't do anything about his quest at all, or Shadowheart might not save her parents because you haven't restored enough of her memories. In Wyll's case you can't just say "You do you" when he has to make a choice about whether to break his pact with Mizora, you have to make the decision for him and he is ok with either. It is not even framed as an impossible choice he can't make on his own through conversation, it's just casually slipped into the scene.