Theory is what matters.

That is the point on which you and I will have to disagree. Theory is useless if it has no bearing on reality.

There's the rub. It can be hard to tell whether theory doesn't have any bearing on reality at the moment due to circumstance, or whether the theory is inherently flawed.

If the theory fails to account for reality in any circumstance, the theory is inherently flawed.

I must say I envy you the clarity of your certitude. It must be nice to live in a simple world. I wish I did.

"In theory, theory and practice are the same. In practice..."

"In practice, nobody knows the first thing about either" is what you meant to say?

You seem to speak as though you do. Have I misgathered you here?

I'm just completing your aphorism.