Keywords: forget (go blank), ignorant, naive
As a Verb or Adjective
1. To completely forget to do something that you should have remembered, or to completely forget what you were going to say next, especially when it is important and potentially embarrassing, e.g., giving a formal talk or acting a role in a play. Idiomatic English = go blank.
2. To not know much about something or things in general and thus to have an empty mind. English = (be) ignorant.
3. To believe that things are much less complicated and difficult than they really are because you do not have much experience of the world. English = (be) naive.
4. To talk or behave in a very strange or foolish way because you do not know any better.