The general rule in California is that you are presumed to have read, understood and intended the wording and terms of a document that you sign, including a will or trust.  It is difficult to prove that someone was unduly influenced, coerced or tricked into signing a will or trust that contains terms that do not reflect that person’s natural intent.  This is especially true if the person committing the undue influence, coercion, fraud or trickery has a close and/or long-term relationship with the person who is signing the will or trust.  So . . . why wouldn’t a bad or greedy person try to inherit by undue influence, coercion, fraud or trickery?  What do they have to lose?  Not much really, assuming that they were not inheriting much anyway if it wasn’t for their wrongful acts.