Before Wagner, people preferred to do it with the lights on: listen to and watch opera that is.
Going to the opera, especially for those who were well-off enough to reserve a box for a season, was mostly if not exclusively about socialising: catching up with friends; buttering up influential and useful people; climbing up the social ladder through being seen with the 'in-crowd' and the great and good.
So an evening at the opera was a light and buzzing bright experience, and the music and acting was a pleasant backdrop to audience members' social lives. It was all very enjoyable (but artistically moribund).
Then Wagner and his music dramas happened and everything, quite literally, got that little bit darker (but artistically more vital).
Wagner's music dramas demanded an audience's complete attention; they did not make good background music. If relegated to such they quickly became intrusive noise rather than unobtrusive ambient wavelets of sound.
Wagner directed that the lights should be dimmed during performances of his works so people would concentrate on the music and drama rather than each other. The noisy and influential box holders complained as one would expect: noisily. They even succeeded in getting German language operas banned from the New York Metropolitan Opera for a year or two.
But Wagner eventually thundered back, and he still insisted on dimming the lights on the noisy box holders. Eventually, after much flickering on and off, the lights dimmed permanently and the minds of many if not all of the noisy box holders were gradually lit up by Wagner's works.
For a new idea or innovation to be accepted and adopted it often needs to be accompanied by a change of practice which encourages different behaviour (dimming the lights led eventually to quiet, attentive and appreciative audiences).
This is not easy to achieve, people resist the change and persist with their comfortable and familiar habits, but being clear about the change of practice and persistent in encouraging people to adopt it will, as Wagner proved, eventually enable a new idea to access and light up people's minds.