Like spokes on a wheel, the various aspect of the many other different areas of law involved attempt to arrive at a hub.  If all of these various aspects are viewed correctly and built properly, with acute attention and detail paid to each spoke as another spoke is tightened, the wheel should - ultimately - roll properly.  Please be aware that these other areas of law include

Most Estate Law problems have more to do with people than law and documents

Know how your Asset Titles (i.e., your own name, jointly, and/or with beneficiary designations).
Know what you are doing before you change ownership or asset titles.
Pick those "in charge" of your Estate Planning documents (your "Fiduciaries") very carefully.
Always remember that laws, taxes, and people change constantly and consistently.