When you encounter an introverted error message, you immediately feel urge to launch your debugger to check what actually happened. The system could be more helpful by being less tight-lipped when something goes bad:

RuntimeException: insufficient funds
	at org.acme.finance.FinanceController.transferMoney(MyController.java:43)

RuntimeException: cannot transfer $50 from ABC to DEF, the source account has only $43
	at org.acme.finance.FinanceController.transferMoney(MyController.java:43)

Lack of information in error messages is often overlooked, because during development you can always rerun your unit tests in debug mode and see all the necessary values. But when an error happens on production environment, then every piece of information is precious, so that you can quicker and easier figure out the cause.

W. Gdela