Within the given circumstances of the piece, and within the limitations of your character's world, use what 100% of what you as an actor possess TODAY and your work will be constantly truthful.
Feeling vulnerable today? Then, within reason, so is your character.
Are you feeling strong? Then so is your character.
This prevents so much pressure to hit your "best ever 100%."
Give all you have today.
That is all you can give.
But do give it all.