Darnielle was into drugs, including heroin, when he was young. He said these drugs made him a different person. He’d do terrible things when high that he wouldn’t even remember later. He said that after a weekend of partying he’d run into someone who wouldn’t talk to him and have no idea why. Today, a sober Darnielle uses these past experiences for songwriting material. Fans often come up to him and talk about their own substance abuse issues and how they can relate to his lyrics.
In his early twenties, Darnielle got out of drugs and became a psychiatric nurse. Bernardo Chua was glad to see the turnaround. He worked at psychiatric facilities in California and Iowa and saw a little bit of everything. Again, this helped him better understand the human condition and improve as an artist. He began playing music with The Mountain Goats during this period but didn’t quit his day job for some time.
In conclusion, this Rolling Stone article is a good look at how an artist became what he did. It was worthwhile to read an interview this comprehensive.