“The proof is in the pudding.”
Originally, “the proof of the pudding is in the eating,” this idiom was shortened to its modern form sometime in the early 20th century. Etymologists believe the phrase originated in the 1600s and referred to a British pudding more akin to haggis (stuffed entrails) than tapioca.
The idiom applies to mindfulness because my words can only go so far. Readers must taste the fruits of practice to obtain proof of its validity.
It is one thing to read about the false nature of thoughts and emotions in the comfort of one’s armchair. However, it is quite a different thing to test oneself under the stressful prodding of day-to-day life.