The doctor's medical notes citing dementia fueled an expensive ($100,000) will contest that ended up going to trial. Even with the doctor appearing on behalf of my contesting sibling and stating under oath that he wouldn't trust my father's opinion on anything, the judge upheld my dad's wishes citing that capacity wasn't in question because there was clear evidence that he not only knew what he was doing, but had his reasons.
Don't feel sorry for the loosing party because as presented at trial, my brother had already received substantial sums of money from out father where I hadn't.