When you sign your will, it's best to do so in the presence of witnesses. Some jurisdictions may even require this. If yours does, then there may be certain criteria for choosing your witnesses. All of these requirements exist to ensure that the testator, or person drafting the will, has testamentary capacity, or knows what they're signing and that no one has undue influence over them.
Some people are more likely to be swayed by undue influence than others. While these cases almost always target someone who is already fragile due to age or sickness, for instance, that does not mean all targets are equal.
A study published in 2015 by True Link Financial suggested that the elderly lose as much as $36.48 billion annually in financial exploitation schemes. As many as two million Americans may be manipulated into giving others access to their assets each year.