Oracle Is Slow, Is There Anything Wrong With Database?

Whenever there is any application slowness or any other performance issue, regardless of source of the problems, the first question comes to DBA that Oracle is slow, is there anything wrong with database?

As a DBA we use to face this situation day to day. This doesn't mean there is no problem from database but many times it could be a server, storage or network bottleneck. May be issue with application coding.