Sometimes the unthinkable happens. Sometimes people make poor choices, which leave them unable to make wise decisions. These can vary from something small, which can be overcome quickly, to something major and life changing, which can take years to overcome. If one of your children is in the middle of such a life changing problem you would not want to them to continue hurting themselves once you pass.
Detailed personalized planning can address those imperfections and assist your children in managing their resources and not allow the imperfections to cause them losses. You can plan the estate so they receive their inheritance in such a way that if they have a drug or alcohol problem or a spending problem, the resources will be distributed to them slowly, allowing them to receive the benefits but not the burdens and therefore not create a situation where they will lose it.