You pretty much summed it up. If you light a fire under someones' butt and their response is to not respond, then it's never going to work. Failing to respond is about as useful as being outright disagreeable, but we don't perceive it as such often because "maybe we just don't know yet, they haven't told us" goes through our mind. When I was in high school, I was in a band that had two gigs per month. The drummer and singer decided that we had arrived and they were going to spend their time smoking pot for half of the practice sessions. We stagnated, and I left. It sucked, but it was the right thing to do. Talented singer and talented drummer, but neither ever focused on anything again. The singer quit singing and worked construction (I guess it's easier to get away with getting high doing that because the hours are pretty set), and the drummer bounced around going through various bands, but never committed to anything. The odds that your current singer will suddenly become a go-getter are pretty close to zero, and if you don't draw the line, you'll be having the same discussion two years from now. The new guy could turn out to be a dud, that's also a risk. But if he is, then you can move to the next person until someone fits.