It isn't saying that there is a duplicate entry in the table already, it is saying that there is already one entry in there with that value for the primary key and it is refusing to insert a second for that reason.
I suspect if you run
SELECT * FORM <table> WHERE <keyfield>='Upping Your Type Game-http://jessicahische.is/talkingtype', or if that key is a composite
SELECT * FORM <table> WHERE <keyfield1>='Upping Your Type Game' AND <keyfield1>='http://jessicahische.is/talkingtype', you will find one matching row, and that your code at the point of the error is trying to insert a second.
Update: dealing with duplicates on insert:
If you try
INSERT a duplicate values for a primary key (or a unique index) you will always get that error. There are a couple of ways around it: check before you insert and either do an update (if something might have changed) or just don't do anything.
There is also the mysql specific
ON DUPLICATE KEY UPDATE option (see http://stackoverflow.com/questions/1218905/how-do-i-update-if-exists-insert-if-not-aka-upsert-or-merge-in-mysql) if you are happy to sacrifice compatibility with other RDBMSs. As of version 9.5 Postgres supports a similar feature with slightly different syntax (
ON CONFLICT DO UPDATE/NOTHING - see https://wiki.postgresql.org/wiki/UPSERT). MS SQL Server, Oracle and some other systems support
MERGE statements as defined (or with extensions) in the SQL:2003 standard (see https://en.wikipedia.org/wiki/Merge_(SQL)) which is intended to achieve the same functionality and more. Be careful with any of these options if cross database compatibility is (or is likely to be in future) one of your goals.