A very nice interview with Merle in 2000:

http://www.bluerailroad.com/archives/haggard_00a.html

a few interesting excerpts from the article

"Music was just something I enjoyed at first. I never thought of doing it for work. Work was something you did outside with a hammer. I never thought I could make my living doing it. I certainly never thought I'd be a Frank Sinatra, or somebody great. I didn't have any ideas like that. But I kept doing it until, when I was about thirteen, all the kids would ask me to come over to their house, or go to a river party with them - we used to have a lot of river parties on the Kern river - and they'd always ask me to bring that guitar. About then I started to realize there was some power and clout in that. And also that I could do something that all those other kids couldn't do. Even the ones with better grades. "{Laughs]

 Another excerpt about writing songs

"Songs don't take a long time for me to write because I don't force write. Most of my writing is done in the morning. If something has offended me or affected me deep enough to touch my soul, sometimes early in the morning things come from somewhere and I write them down. Sometimes I'm as surprised when I write them down as anyone who hears it. There's a certain amount of talent you develop in writing songs. Methods and ways of proving whether a line should be there. The best songs I've written, like "Mama's Hungry Eyes" or "Mama Tried" came so fast I could hardly hold the pencil. I could hear the whole song, and I would just try to get it all down before I forget it. There is no doubt that songs are gifts. People who don't believe in another dimension, a higher plane of existence, have never written a song. Or have never had songs given to them. I've read some songs back and wept."