max_seeks_for_key not working

The query optimizer is not selecting an index to read table and is instead doing a full table scan. I want to force the query optimizer to use an index. I have set the max_seeks_for_key to 1. When I do an EXPLAIN on my query, it shows that there are "possible keys" but it still chooses to do a FTS. So setting the max_seeks_for_key has no effect.