Oh fun. I'll be honest none of my quotes are from authors though. Unless you consider vocalists who write their own lyrics to songs as authors.
Most of these following quotes have to do with being self motivated.
You're just sliding painfully back
If you're not striving forward
-Own Your World, by Hatebreed, lyrics by Jamie Jasta
No sleep, no rest, do anything it takes to be the best. No sleep no rest, must stay driven I can't relent
-Looking down the Barrel of Today, by Hatebreed, lyrics by Jamie Jasta
I used to be really lazy when it came to forward progress on my work. I absolutely have to surround myself with things that make me want to keep pushing on. Jamie Jasta's lyrics in most of his songs are about becoming better, or rising above adversity. They really resonate with me, and I could probably drop several more, but I'll spare you all.