where the rubber meets the road (e/u)

I am still searching for meaning.

looked it up in the Google
28800 hits make it a widely used but unidentified idiom.

Втр, 2004-10-26 19:58 — Fenya
the nitty-gritty

here the rubber hits/meets the road - where the theory is tested, when the action begins; the nitty-gritty

Example: In the workplace, you apply what you've learned - that's where the rubber hits the road.

Also from PainInTheEnglish site
« Where the rubber meets the road is where the real work happens. Implication is that the rest of the car -- rear window, seat belts, radio, etc. -- is less relevant to motion than the tires moving down the road. It’s routinely used in large organizations to remind senior managers that where the organization deals with its customers is where the rubber meets the road. Is there a simple example, hmmm? Um, the people who process applications for social security and mail out checks are where the rubber meets the road, and the HR dept or receptionists are (important, don't get me wrong, but) less relevant to the impact of that mission on customers.»

See also here
info.study.ru/?open=3b57d08f.16051