This is the same principle as the:
“Map is not the world,” or “All models are inaccurate by definition.”
As Mike Tyson put’s it, “Everyone has a plan until they get punched in the face.”
The reality is that there is a significant difference between: theory, the idea, the plan, the map – and – practice, the execution, the battle, the world.
Differences in events, environmental conditions, relationships, dependencies exist in practice. Which is probably why it’s called practice.
Whilst you begin with the theory, you execute with practice. Can you play a guitar without knowing guitar music theory? Technically yes. Of course, knowing the theory will improve your technique immeasurably. But knowing the theory is not enough.
Expecting practice (the execution, the battle, the world) to be exactly like the theory is the chief cause of stress!!
Think about it.
Every time you’re stressed. You have a mental model, a theory, in your head and something in the real world doesn’t match the theory. That’s (always) it. You have a theoretical expectation of someone, or theoretical plan to achieve something, or theoretical idea about customers, or driving, or …
…and the practice no longer matches the theory.
The trick is to let go the theory. Centre on the now. Accept the reality of the universe.
Because the only place there is no difference between theory and practice, is in theory.