I have spent hours of days in surgery. I realize how tiring a surgeon gets dissecting and stitching back together a human body, removing the cancer that has invaded the body.
The cancer, in my tree, began when I was a "newbie" to genealogy and didn't realize that when I added a person to the tree, that I needed to make sure that person wasn't already in the tree.
Of course, in our family, a lot of the generations before us had married relatives from other parts of the tree. By adding them as new persons, I was making duplicate entries of the same person. These"doppelgangers" are the cancer that has invaded my tree, that is taking me years to remove.
If I had any advice to give to someone that is starting to take up genealogy, it would be to make sure the person is not already in your tree. Check and double check so that you don'r get "doppleganger cancer" that takes forever to remove.