Let us get an overview of query hints.
We can specify hint using /*+ HINT */ as part of the query.
Make sure there are no typos in the hint.
If there are typos or there no indexes specified as part of hint, they will be ignored.
In case of complex queries, CBO might use incorrect index or inappropriate join.
As an expert if we are sure that, the query should be using a particular index or right join, then we can force the optimizer to choose such index or join type leveraging hint.