When most people think of accidental disinheritance, they naturally think of a faulty will. In this case, many people have neglected to create a valid will in their local jurisdiction. This can occur, many times, when they use an online will-creation service.
Some of the ways to create a faulty will is to not sign it properly. The other way, in Kansas, is to not have at least two signatures (although it should be noted that other jurisdictions require three signatures). Finally, it is good practice to get the will notarized so that it can be self-proving when in probate.