Since my dad was adopted, half of my pedigree is yet to be discovered; however, since I have my mom's family tree and DNA - and with the phasing utilities available - I've been surprised to find that my ex-husband (yes, I have custody of his DNA as well!) seems to be matching to a lot of my dad's presumed cousins. Yet, my ex and I share no DNA, so any connection has to be quite distant.

Also, I found that my ex's paternal grandparents were 8th cousins. Then again, both had ancestors coming out of pre-Colonial New England.

On the other side of the coin, you may find documentable, paper-trailed cousins that you share no DNA with whatsoever. I discovered one of these recently. While this cousin and I have a third cousin in common, and all three of us have DNA matches to a common ancestor, AND he shares my mom's very uncommon surname, he has no DNA in common with me or my mother. DNA is just that random.