Inheriting property does not always bring out the best in family members. Many people, of course, handle everything smoothly, following a loved one's instructions as much as they can and peacefully agreeing on the rest. But a death can raise long-dormant relationships issues and revive old jealousies and resentments.
Probably the one element most likely to provoke bad feelings is surprise. If everyone in the family knows the broad outlines of how you're planning to leave your property, they may understand your choices. Even if they don't, they will have had some time to get used to the idea and air their concerns. They are likely to respect your choices, and not try to undermine them informally or through a lawsuit.
If, on the other hand, your estate plan takes everyone by surprise, there could be confusion, argument, and possibly court fights. Say, for example, an elderly man leaves the lion's share of his estate to a charity or to a caregiver who recently arrived on the scene, or a woman leaves a valuable piece of art not to her children but favors a niece who wasn't known to be particularly close to her. If the children knew that the niece had a special connection to the artwork, or that the caregiver had performed extraordinary services, they wouldn't be left to wonder at the fairness of the bequests.
Even more common is the hurt caused by an unequal division of assets among offspring. Most parents leave their property to their children more or less equally, but there can be many good reasons for a different plan--perhaps one child has problems handling money, or already received an "advance" on his inheritance in the form of a gift. As long as the children all understand the reasoning, they are likely to accept your decisions. After all, it's your money.