You've put quotes on your field names. That forces MySQL to treat them as strings, not field names - and you can't insert into strings.
INSERT INTO articles (word, group, selfnote) VALUES (....);
is the correct syntax. The only quoting type allowed on field names is the use of backticks to escape reserved word fields, e.g.
INSERT INTO articles (table, int, varchar) ...
would fail due to the use of 3 reserved words, but adding backticks
INSERT INTO articles (`table`, `int`, `varchar`) ...
makes them acceptable as fieldnames.
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