Oracle Solution for Error ora-04091

ORA-04091: table string.string is mutating, trigger/function may not see it

What triggered the Error:

A trigger (or a user defined plsql function that is referenced in this statement) attempted to look at (or modify) a table that was in the middle of being modified by the statement which fired it.

What should we do to fix it:

Rewrite the trigger (or function) so it does not read that table.