When a Leaf is not YOUR Leaf
Sometimes we get so wrapped up in clicking on every single hint for our ancestors that we don't stop to think that there may be more amiss than is right with the hint. In my experience, about 1/3 of the leaves that I investigate are NOT related to the person I am researching. I always look at each hint from a skeptical viewpoint and if there is even a hint of truth to it, I use the "undecided" button and then come back to do further research later. That way I don't lose the thread or the information, but I'm not adding false information to my tree.
I treat other researchers' trees with more skepticism than other (more official) documents because so many people just keep adding relatives even if they don't have a primary source to back it up. Finding the primary sources like birth and death certificates and census records are the best way to confirm any hints. BUT--many primary sources are also inaccurate or cryptic.
The information on death certificates is always 2nd hand from a child, spouse, neighbor or someone who may only be getting their information from years and years of celebrating a person's birthday on a certain day or thinking they were born in a certain year. (Due to the taboo of having a wife who is older than her husband, many times women would lie on marriage and census records to make themselves seem younger than their spouse.)
In the case of census and immigration records, often times with early immigrants, there is a language or accent barrier or lack of formal education that creates spelling and math errors in peoples' names and ages. And the census taker's chicken scratch can be maddening to decipher. For instance, take the last name Lee. If handwritten, it could look like Lu or Lii. I saw a hint for a Daniel Lu and thought there was no way...but it was. The census taker was just a sloppy writer.
Sometimes it is a leap of faith to add a hint and it is a chance you should be willing to accept as long as you go back and delete it when you know it isn't accurate. I keep my trees private so that my "work" isn't muddying the waters and I only make them public once I'm sure that the info is correct. After all, I have several Irish ancestors in my family who will haunt me for decades if I create inaccuracies in my research.