Short answer
Swallowing means catching an exception and doing nothing (or just logging and continuing) so the failure is silently lost — a leading cause of undebuggable production issues.
Explanation
The right patterns are: handle it meaningfully, rethrow, or translate it to a higher-level exception while preserving the cause via the chaining constructor (new ServiceException("...", cause)) so the stack trace survives. Never catch Throwable/Exception broadly to hide problems, and never catch and lose the cause.
Common mistakes
- Logging and rethrowing at every layer, producing duplicate stack traces.
- Throwing a new exception without passing the original as the cause.