If someone is your ancestor, they were born (hard to avoid that), they reproduced (married or not), and eventually died (hard to avoid that as well). Everything else is somewhat negotiable–within reason.
Everything else you “think” that is true about them may not be true. This gets especially true as your research extends back in time and what a person “knows” often is based more on what we assume as opposed to things we have evidence for.
They might not have attended the same church their children did. People change churches for a variety of reasons.
They may have spelled their name differently than their descendants do or did. They might not have really cared how it was spelled.
They might not have been a member of the ethnic group their children thought they were. Ethnic prejudice might have caused them to indicate they were from somewhere other than where they were actually from.
Every detail Grandma gave you about her heritage might have been 100% correct. Or it could have been 100% false. The reality is usually somewhere in between.