It's very tempting to add an ancestor to your family tree when you find him/her in someone else's tree. You get so excited that you are very likely to just start adding. But wait! Do they have a citation that you can verify? I have seen trees in Ancestry with possible ancestors and after I study them I have realized that they have added my ancestor but went up the wrong line. In other words, they barked up the wrong tree. Do not ever add someone to your tree without verifying that he/she is the right one.