An intervention reorganizes the family (and friends) to extend help in a way that is possible for the impaired person to receive.
An intervention is an orchestrated crisis designed to help a person who needs help to accept it even though s/he is convinced s/he doesn’t need it. This kind of denial is usual in the presence of an addiction (to a substance or behavior). It can also appear when a defense system has been reinforced over time — e.g. an elderly person afraid of change and resisting going into assisted living.
The secret of an intervention is Numbers — the concentrated caring energy of a whole group representing significant parts of a subject’s life. A troubled person can easily deflect one concerned person, but a group has unique power to reflect back to the suffering person the goodness and value s/he had come to doubt. This process is how Betty Ford (wife of the former President) was gently persuaded by her family and friends to enter treatment and begin a new life of recovery, a life which has blossomed for the benefit of many people beyond her own family.