Why were most of the Germanic kingdoms short-lived?

Because they were founded in the course of hostilities and were very unstable. Civil strife or wars with other states often broke out there. The only barbarian state that was able to go through a long and difficult path of change was the kingdom of the Franks. It was created back in 481.

One of the components of a person's success in our time is receiving modern high-quality education, mastering the knowledge, skills and abilities necessary for life in society. A person today needs to study almost all his life, mastering everything new and new, acquiring the necessary professional qualities.