Keep in mind that there’s not always a “need” for a record or a document. If a child has no “estate” or inheritance from a deceased parent, there will not be need to appoint a guardian. If an ancestor doesn’t belong to a church, his children probably won’t be christened there. If an ancestor does not own property, there will not be property tax records. If recording births was not mandatory when a relative was born far from the county seat, there might not be a record of their birth.
If your ancestor didn’t care about his reputation among his neighbors, he probably didn’t bother to have his biography included in the local county history.
It doesn’t mean that we should fail to look for records, but to keep in mind that sometimes there are pretty simple reasons why records do not exist.