The Rubber Meets The Road Meaning

Example : Used other than as an idiom: see rubber,‎ meet,‎ road.1928, How to avoid automobile accidents, page 30:  Even 500 feet probably wouldn't allow you to brake to a stop, because it's "where the rubber meets the road" that counts.1957, Max Shulman, Rally 'Round the Flag, Boys!:  Now we're getting down to where the rubber meets the road.2002, F. Stevens Redburn, Public policies for distressed communities revisited, page 159:  It can only be judged "when the rubber meets the road"; when its implementation does or does not produce results.2007, Dan Miller, 48 Days to the Work You Love, page 85:  It is in the interview that the rubber meets the road.