“My area of research is something that in all fairness has no practical usability whatsoever and the thing is I'm often asked to apologize for that. It is interesting to me that people ask 'what's the point of doing that if it's not useful?' But they never ask that, or do they very rarely ask that about art or literature or music. Those things are not gonna produce a better toaster.”

Turning Pages: The Life and Literature of Margaret Atwood (2007)

Posthumous attributions, Tupac: Resurrection (2003)

Letter to Robert McAlmon (4 September 1943), published in The Selected Letters of William Carlos Williams (1957) edited by John C. Thirlwall, p. 217
General sources
Context: Why do we live? Most of us need the very thing we never ask for. We talk about revolution as if it was peanuts. What we need is some frank thinking and a few revolutions in our own guts; to hell with what most of the sons of bitches that I know and myself along with them if I don't take hold of myself and turn about when I need to — or go ahead further if that's the game.

Variant: I always say, better ask forgiveness than permission.
Source: Eragon

Raised by Wolves, season 1, episode 4. Character Mother.

and they look at me blankly, unable to articulate the answer. It’s not that they don’t want things, it’s just that they don’t have a high level of clarity regarding the matter.”
Popular Quotes, Essentialism: The Disciplined Pursuit of Less, Journal Articles

Source: What I Talk About When I Talk About Running

And that last bit I think often gets missed out.
Interview at the Academy of Achievement (23 May 1998).