If there were a single portal through which every beginning genealogist had to pass, I would plaster Dick Eastman's recent post, "Barking Up the Wrong Tree," all over its walls in a jumbo-size font.
Eastman's story is good because it's so familiar. We've all done it, and more people are doing it every day (encouraged no doubt by Ancestry.com's ignorant advertising): assume that if the name's the same, the person's the same -- and then when we later find the mistake, have to remove not only the wrong person but all the work we did on that wrong person! He asks readers, "Have you independently verified every 'fact' you have discovered? By 'independently,' I mean that you should always find a contemporary record that agrees with the first record you found."
I would add the suggestion that knowing and following the five-part Genealogical Proof Standard is a good way to avoid getting into this fix:
- a reasonably exhaustive search;
- complete and accurate source citations;
- analysis and correlation of the collected information;
- resolution of any conflicting evidence; and
- a soundly reasoned, coherently written conclusion.
Dick Eastman, "Barking up the Wrong Tree,"Eastman's Online Genealogy Newsletter, 14 July 2012, http://blog.eogn.com/eastmans_online_genealogy/2012/07/barking-up-the-wrong-tree.html
Harold Henderson, "STOP Creating Former Ancestors!," Midwestern Microhistory: A Genealogy Blog, posted 15 July 2012 (http://midwesternmicrohistory.blogspot.com : accessed [access date]). [Please feel free to link to the specific post if you prefer.]