Two fairly recent Tennessee undue influence cases prove a point: To win an undue influence case, the plaintiff (or contestant if it is a will contest) must prove more than mere unfairness or favoritism.
Both cases involved alleged undue influence with respect to deeds for land. In the first case, Bunch v. Bunch, a mother owned 35 acres of land. While the mother was alive, she deeded about half of the acreage to her daughter. At her death, the other half of her land passed to her daughter and son equally.
After the mother passed away, the daughter brought a partition action to have the land which was left to her and her brother jointly sold and the proceeds divided. The son filed a counterclaim against the daughter, his sister, in which he alleged that the deed wherein his mother transferred half of her land to her daughter was the result of the undue influence of the daughter.