ora-01704: string literal too long
 *Cause:  The string literal is longer than 4000 characters.
 *Action:  Use a string literal of at most 4000 characters.
            Longer values may only be entered using bind variables.

SQL> var my_bind_variable varchar2(100)
SQL> begin :my_bind_variable := 'my value'; end;
  2  /

PL/SQL procedure successfully completed.

SQL> declare
  2    my_bind_variable varchar2(100);
  3  begin
  4    my_bind_variable := 'my value';
  5  end;
  6  /

PL/SQL procedure successfully completed.

...

SQL> declare foo varchar2(32767); begin null; end;
  2  /

PL/SQL procedure successfully completed.

SQL> declare foo varchar2(32768); begin null; end;
  2  /
declare foo varchar2(32768); begin null; end;
                     *
ERROR at line 1:
ORA-06550: line 1, column 22:
PLS-00215: String length constraints must be in range (1 .. 32767)