"Now here's where I'm going to alienate everyone in the room. Television is bad for creativity. So is music.  Not small 'b' bad.  Capital 'b' Bad. A professional golfer does not catch up on the Young and the Restless while he walks up to the fairway to take his second shot. Football players on the sidelines are not listening to Pink Floyd's Dark Side of the Moon on their walkmans. A concert pianist does not listen to Terminator 2 while he practises a concerto. If you would even suggest such a thing to any of these individuals they would tell you that you're two fries short of a happy meal. Divided focus is no focus. All of you disagree with me but that's okay, because I'm right and you're wrong. Divided focus is no focus. Focus precludes both companionship and the illusion of companionship. Isolation, silence and the training of all of your faculties so that all that exists for you is the feel of the pencil or the pen, the subtleties of pressure of that pencil point or that pen point, to the exclusion of all other stimuli, is a universally ignored but self-evident route to improvement."

Full text here:  http://momentofcerebus.blogspot.com/2013/04/advice-for-would -be-cartoonist.html

It's funny Sim uses athletes and musicians as examples to support his opinion and not writers, painters, architects or others whose jobs are to sit by themselves at a desk and not performing in a public venue. 

As far as listening to music as being capital B-bad, it didn't seem to hurt Jack Kirby's creativity any. Everyone has their own way of working, there's no right or wrong as long as the work gets done.