Property passes three ways on death - by will, by contract, and by operation of law. Many people pay close attention to the state of their wills, keeping them updated as situations change. Passage of property by operation of law is something over which most people can exercise little control.
Property passing by contract most commonly consists of life insurance policies, IRAs, pensions and other deferred compensation arrangements, and joint bank accounts (or so called "Totten Trusts" or "i/t/f" accounts). In these cases, the passage of property is controlled through the designation of beneficiaries who will take the property upon the death of the owner.
For various reasons including death, divorce, or simple change of mind, the beneficiary named at the time the insurance policy is purchased or when the IRA, 401(k) or pension plan is established may not be able to take the property or may not remain the person the owner wishes to receive the property upon his death. Failure to keep beneficiary designations current with the owner's desires can lead to undesirable and sometimes embarrassing problems. At best, this failure leads to unnecessary complications in estate administration. These problems are entirely avoidable through a little periodic checking.
So review those insurance policies from time to time. Check your IRA and pension beneficiaries. Be sure that the persons shown as beneficiaries in the documentation are the persons you want to receive the benefits on your death.