Do you have any idea how disruptive it is to the family, close friends, to "spill the beans" about something like that?
Considering that I was right in the middle of it at age 10, I do know a lot more about it than anybody who didn't. Dad went to prison, and destroyed his college professor career for the rest of his life after getting out. Mom divorced him a few years later. Older sister (the victim) went into foster care for 5 years (longer than Dad's time in prison!). I was left for the next 7 years living in a much poorer family that was essentially broken, and in the later half of that living with "a sexual psychopath unlikely to benefit from treatment" (the psychologist's words at sentencing). I got the hell out of there at age 17, probably the least-damaged family member.
Of course, I don't blame my sister at all. Never did. It was 100% his fault. Her getting the authorities involved was absolutely the best thing possible, even better than him dropping dead from a heart attack. Her going into foster care was even a positive thing, because of my step-mother blaming her and the fact that she had one set of very nice foster parents.
BUT STILL: She was a perfectly normal, seemingly well-adjusted little girl and then teen during the time they were having sex. She was a Camp Fire Girl. She got excellent grades in school. She had no abnormal behavior. She had normal emotional health. She had a normal relationship with her little brother. She did tell me years later that she knew the sex was not normal, and hoped it would stop when Dad remarried my step-mother. But the fact that it didn't was not distressing enough to make her act on it for five more years.
Around this same time, I was a normal 10 year old boy. My sexual behavior was mostly solo, but not exclusively. I played "you show me your's" with my contemporaries, both male and female, and discovered that I found girls much more sexually attractive than boys. Some of those girls were quite enthusiastic, which informed me that 1) girls can enjoy sexual attention, and 2) girls are sexually developed before boys. So I was not surprised when my 13 year old sister told me she was having sexual encounters and enjoyed the physical sensations. My younger peers and I did the same thing. We didn't perform the same physical acts, simply because we didn't know about them.
This is why I felt, and still feel that the sex was not a big deal, and the psychological manipulation was much worse. Having sex with an adult was bad. Having sex with your own father was worse, though he avoided anything that could make incest babies. Having your own father brainwash you into thinking this was some "special relationship only the closest, most loving fathers and daughters shared" was worst of all: The ultimate betrayal.
