Why feeling is not the actor's starting point
Action, circumstance and a scene partner are repeatable tools. Feeling is a result, not a command.
When you try to play sadness or anger directly, you often start watching yourself instead of engaging your scene partner.
Start with a simpler question: what do I want from the other person, and what am I doing to get it?
When the circumstance is specific and the action has an effect, feeling can emerge as a result rather than a display.