This statement sounds SO self-evident, like.... the sun comes up in the morning, in the east.
However,... part of the issue is the genealogical definition of "known." For this genealogist, "known" equals solid evidence of the particulars of a person, from careful examination of documents and analysis and ...
My father knew that his gggreat, Patrick Ross, was killed during the Civil War (Union), and he wanted to find the parents of Patrick. Off to the National Archives in DC (close by since he lived in northern Virginia) to have a look at Patrick's compiled service record, and, as it happened, his wife's widow's pension.
By that time, I had attended a number of genealogy seminars, and had a basic working knowledge of how this world worked, and we made a day of it.
Dad, a lovely and intelligent man, who spent his working life analyzing complex cross-cultural questions, was totally disappointed in the information offered by the thick pension file. As he read each page, he would shake his head saying, "It doesn't say who his parents are." I heard this at the end of almost every page, and when it wasn't said, the head would shake, saying the same thing without words. I however, was totally delighted with the pension record. As said, it was huge, with pages and pages of depositions by everyone in the area. I "met" the people in the neighborhood (think FAN club), and got the married names of the daughters, and one deposition was even given by James Shirley, who said he was married to one of the daughters. Pay dirt on any number of points -- at least as I was concerned.
Fast forward about 30 years, add unnumbered hours of research, and I have a working hypothesis about Patrick Ross' father. Is it proved? Not yet.
But the joy is in the search.... right??
and stay tuned... Patrick et familie may make an appearance from time to time (GRIN)