It takes only a moment to step over the line, especially when no one knows exactly where the line is. In my case, it started with a visit from my old friend the activist. The activist became my patient back in the mid-1990s, when H.I.V. was slowly morphing into a treatable disease. He was young then, with a mop of dark curls — excitable, suspicious and frantic about his health. He was convinced the new drugs were pure synthetic poison, a profiteering scam by the government and Big Pharma. He was also feeling sick enough that he thought he might just give them a try.