Collection of genealogical material divides into two main sources: primary and secondary. Primary sources include vital records, church records, censuses, wills, military records (muster rolls, enlistments, discharges), land deeds and grants. Secondary sources come from published town histories, published family genealogies, hearsay information gathered with no supporting documentation.
The strength of any genealogy is the documentation. Primary records are always preferred over secondary sources. That's because secondary sources are just that — secondary. It usually comes from a third-party source. The information could be accurate or inaccurate, but may be "unsupported" — that is, not proved with vital records, wills, etc. Primary records usually have a direct link to the ancestor. A child's birth certificate contains information provided by the parents; marriage certificates includes information supplied by the bride and groom; information reported on death certificates usually comes from a close kin member.
Even primary records may contain errors so it's important to gather and compare additional primary source information. The more supporting evidence you collect, the stronger the facts become in our own genealogy. This is especially important if you intend to join a society such as the "Daughters of the American Revolution." Primary records become the key to your acceptance. In you cannot prove, for example, that your ancestor fought in the American Revolution, then your application would be denied.
So take the time to analyze the details of the information you research or you will be barking up the wrong tree.