One of the pitfalls in Oracle is the fact that sometimes you can select from a table if you run a query in SQLplus but that you can't when running the query from a stored procedure. In order to run a query from a stored procedure you need a direct grant for the object and not a grant obtained through a role.
If I see a table in the all_tables view, how can I know if I can see this table because of a direct grant or because of a role grant?