Nothing in the world can ever go as smoothly as we like. This happens in all aspects of life and even in the world of adoption. Occasionally, a child gets adopted into a family and it doesn't turn out to be the right move. There could be a number of factors that could lead to an adoption dissolution. This is often called "unadoption".
Adoption dissolution isn't very common when it involves a newborn or infant. It becomes more frequent with foster children who have problems adapting to their new environment and other family members such as siblings.
Siblings might tease the adopted child constantly or the adopted child might be very mean or abusive to new family members. Often this can be resolved through counseling or other forms of behavioral modification but not always.
Older children sometimes have a history of being adopted many different times by various families. This doesn't mean they are bad children but could be due to medical issues.
ADHD and reactive attachment disorder can cause problems for adoptive parents who don't understand these disorders completely and just can't deal with them.
Sometimes adoption dissolution is the only choice so the child can find a family better equipped to handle their special needs.
Sometimes, the child might ask for an adoption dissolution. In some states, the law allows children to request this if they are at least 14 years old. The end result could place them back into a foster home or with some other relatives. This is a very emotional event that can affect parent and child alike but may be unavoidable.