The Oracle database system is quite complex relative to other database systems. This tends to create a few problems:
It turns out more difficult to manage than many expect.
Misinformed people purchase it because of its reputation for power in big companies even though they are not a big company or don't need so much scalability. However, they may be biting off more than they can chew. Sometimes you just need a NimbleDatabase, or something mid-sized like MySql, PostgreSql or SqlServer.
Exposure to Oracle's complexity taints people's view of RDBMS as too cumbersome.
Other DB products try to copy aspects of Oracle, but don't always copy the right aspects for their target market.
Now don't get me wrong, this topic is not Oracle-bashing necessarily. Oracle is a very powerful tool that has lots of options because it is used in a lot of large organizations with complex and large-scale needs. It serves this market well and it is difficult or impossible to compete with a well-tuned Oracle system on scalability. (Only IBM's DB2 seems to even try.)
As a general rule, BigIronAintCheapCategoryDatabase, CategoryVendorOrBrand?