I must be from Mars because as a steady working bass player for the past 25 years I have NEVER developed callouses on my plucking fingers, no matter if I've played flats or rounds. I also use a little fingernail (about 1/16") and a fairly light touch. I get a good thick tone, or I can get a thin tone. When I played upright I had a little bit of callous, but I was playing classical music and pizzicato lines weren't the only lines to be played. Most of it was arco. On electric I can play all day and night without any problems whatsoever excpet for my muscles maybe getting tired. Four-hour gig? No problem. two gigs back-to-back? No problem.