In theory, the difference between practice and theory is due to practical considerations that theorists find it impractical to fit into their theories.

In practice, theory uses the practice of theorizing about practical matters, while not noticing that the theoretical method practically distorts the theory beyond application to practice.

Theoretically then, the practical facts are that theory is in practice good for predicting what happens in theory, but impractical as a theory with direct implications for practice, except where theory states that the practice is sufficiently close to the theory to make any difference, for all practical purposes, theoretically zero.

In practice this does not happen very often.