Insert results in 0 1

[Sherman Willden]

Computer HP Compaq 6710b
Development Platform: Ubuntu 17.10 mainly command line work
Tools: perl 5.26 and postgresql 9.6

Why do I get a 0 1 when using insert?

Thanks;

Sherman
classical=# INSERT INTO string_groups VALUES('et_b_02', 'Sonata in B
minor', 'Eroica Trio', 'Jean Baptiste Loeillet', 'Baroque');
INSERT 0 1
classical=# INSERT INTO string_groups VALUES('et_b_02', 'Sonata in B
minor', 'Eroica Trio', 'Jean Baptiste Loeillet', 'Baroque');
ERROR:  duplicate key value violates unique constraint "string_groups_pkey"
DETAIL:  Key (id)=(et_b_02) already exists.