It's the second one that's hard if the first book didn't sell well. I don't think a first novel that one wants to publish in hardcover should be published in trade paperback. Publishers must also be patient. Weyr says that trade paperbacks have not been published in an intelligent or logical way. But it doesn't always.
Publishers are notoriously bad in figuring out their markets.
Trade paperback lines which aren't instantly successful have also caused problems for paperback editors. This is not because the people are inadequate, but because results haven't been magical. Publishers would be more successful if they really thought it through. Publishers have to learn to pinpoint markets and promote books. They don't do that.