The headline is an edited quote - the original one is from Quincy Jones, and it's "My feeling is always; leave at least twenty to thirty percent of room for the lord to walk through the room". He says it about recording in the studio - you enter the studio with a plan; the melody and lyrics, but you should leave room for the unexpected - usually that's where the magic happens. A lovely example of this is when Luther Vandross by chance was in the same studio as David Bowie when Bowie recorded Young Americans. Luther loved the song but thought it lacked harmony, and he started to sing the legendary back vocals "...Young Americans, we where young..." Mr Bowie stood up in the studio and said: "Who sang that?", and the rest is history.
The projects where I can relate to this are for example film or photo sessions. Usually, there is a plan; the script and the storyboard as guidance, but because productions are so expensive you can more or less only prepare mentally and through discussion. It's not until the moment when the crew and set are in place that you can start to explore the possibilities of how to best capture the material.
Where am I heading with this? - There is so much that happens in the process; creative work demands enough room to explore beyond the brief to deliver something extra. Quincy's thought about the creative process summarises this in those few words.
See the film Quincy on Netflix! It's just a fantastic portrait of one of the most generous and brightest musicians in our modern history. If you are curious about the story behind Young Americans, listen to P3 Soul at little over nine minutes in.