I frequently talk to people who have "inherited" their genealogy from a relative. I fall into this category. I probably have mentioned this before, but it is worth reviewing. I had the usual casual contact with the idea of genealogy and family history while I was growing up. The most obvious manifestations of genealogy were several surname books in our home library, about branches of the ancestral lines. I was marginally familiar with these books, because I used them from time to time to try and figure out how I was related to some of the relatives that I met or knew about. One of my very distant relatives was a prominent leader of The Church of Jesus Christ of Latter-day Saints and so I often got questions about how I was related to "President Tanner." Every so often, I would go back and try and review the connection.
In about 1982, I was given an assignment, along with everyone else in the Church, to update my family history and submit the four generation family group records to the Church. Up to this time in my life, I had been told repeatedly, that "all my genealogy had been done" either by my maternal Great-grandmother or by my paternal Great-grandmother. It is a long story about how I finally got involved which I will not repeat here, but suffice it to say, it took me only a short time doing research to figure out that the story I had been told about all the "genealogy being done" was not true. Finding out that one fact, starting me on my 30+ year journey that brings me to where I am today.
The main issue that I was confronted with was that the dates, places and names I inherited from my genealogically-inclined relatives formed a huge pile, almost two feet high, of family group records. I systematically went through each family group record for consistency and verified anything that appeared doubtful. That took about 15 years.
Now, with that background, what do you think I am going to say to people who walk in with thousands of names in a computer file?
My first rule, as I pointed out, is don't believe anything you inherit from others. A healthy sense of skepticism is a necessary ingredient to correcting the errors of the ages. The only qualification on this skepticism is if the information is documented with a source that can be verified. A citation to someone's family group record doesn't count as a verifiable source. Do you think that I have been able to go through the thousands of names I inherited and verify each one? Why do you think I keep working on my genealogy? Actually, the situation has gotten worse over the years instead of better. With programs such as FamilySearch.org's Family Tree, I can now see all of the different opinions about my family lines. The amount of misinformation is overwhelming and simply sourcing my direct lines is going to take quite a while.
Start with yourself, your parents, your grandparents etc. and work your way through each of the entries in an inherited genealogy. If there are now sources, try to verify each date and fact in the database. Keep working your way through each generation on all your lines until you find that the verified sources disappear. That is where you begin your research. The tendency is to make a leap out to the first missing ancestor. The problem is that the researcher may not even be related to this person. The mistakes in the pedigree may start several generations down from the missing ancestor.
Having a huge number of people in your file is nice. You can get the same effect by copying old phone directories, with about the same degree of certainty as to the relationships. Do your own work. Cite your sources so the next generation doesn't have to do the work over again.