What you say about Kurt Cobain, reminds me of the "Flow State" or what basketball players call "Be in the zone".

I think it's Jordan Peterson , the philosopher/sociliologist talks about it. Basically, when you perform art, or sport, there's a moment where the universe and everything around you align, this is when great things happen.
The fighter/actor Bruce Lee called it the flow state, it's more about feeling and not overthinking it, be like water.
And I think that what Kurt was talking about, I am sure it happened to you in the past, you're gigging with friends and colleagues, and all of a sudden, everyone is playing at their best, it's almost like a spiritual experience. that transcend music.

It's impossible to be constantly in that state, it cannot be forced, or emulated.

The fact that Kurt was about to record, he didn't have time to overthink about the lyrics.

Some of the best mistakes in music, became trademark songs.
The whistling for the song "Sitting On The Dock Of The Bay" by OTtis Reddin, was a pure accident, he just forgot the lyrics of the 3 rd verse.

Same for the song Ain't No Sunshine, by Bill WIthers. He starts singing repetitively "I know I know I know I know", and he just forgot to write a verse for that part. They kept it and now the rest is history.