A theory must be followed by practice.

Source: Tatoeba

Those of high wisdom, when they hear the "Way", strive to practice it; those of moderate wisdom, when they hear the "Way", are half-believing and half-doubting; the ignorant, when they hear the "Way", mock it. If the "Way" is not mocked, it cannot be called the true "Way".

Source: Tatoeba

Putting ideas into practice is difficult.

Source: Tatoeba