Here are two stories from my files (not real names):
The Jordans created a revocable living trust and made wills that gave all of their assets to the trust. Later, they revoked the trust because they never used it properly and it was too complicated to manage. But, then Mr. Jordan became mentally incapable of revising his will. So his will which gave all of his assets to the trust is largely invalid. It was too late for him to revise the will to correspond to changed circumstances.
Sally, a single elderly lady refused to give her power of attorney to one of her adult children. Now, she is in failing health and has impaired mental abilities. She lacks the capacity to give her power of attorney to anyone. She's going to need a court appointed guardian to manage her affairs.
When a person drafts estate planning documents such as a will or power of attorney, they must have the mental capacity to convey their wishes to an attorney and understand the documents being prepared. There does come a point when it is too late - when the client no longer has the mental capacity to understand the documents.
Lesson:Don't wait. Do your planning now while you are feeling good.