[whizzter]

That's exactly when a GOOD debugger becomes useful, if you can get an hint at what's wrong you can often (if needed and the fault wasn't caught by the debugger) put in a good conditional expression for the breakpoint and only break once it fails, yet if every input looks fine and your code isn't a mutating mess you can set a previous line as the next statement and re-step what happened to create the error condition for the particular object.

Adding traces (probably over several iterations to narrow down things), rebuilding, rerunning and inspecting those traces would've probably taken multiples of the time to build and run everything up to the point of failure.