I've learned that I get blocked when my subconscious mind is telling me that I've taken the work in a wrong direction, and that once I start listening to what my subconscious is trying to tell me, I can work out the problem and get moving again.
It's a tough job to tell a story when the audience already knows the ending, and the ending is bleak.
For every SF reader of that period, Robert A. Heinlein was also a touchstone.
The Rift, which was well over a thousand pages of manuscript, took two years.
I'm not afraid of werewolves or vampires or haunted hotels, I'm afraid of what real human beings to do other real human beings.
The mass-market paperback, for one, is too expensive.
