Useful exception description are not shown not shown when database configuration is incorrect, for example, logs show that

When SID is incorrect, log reports TNS:listener does not currently know of SID given in connect descriptor
When '@' delimiter is missing on Resource URL between thin and URL Io exception: The Network Adapter could not establish the connection

It might be useful for troubleshooting purposes to print out exceptions (though probably not the full stack trace) when the database connection fails.