Your nightly build is red. There are some test cases failing and you know that this should be the moment when you need to stop and investigate. Your Product Owner runs in the team room and start to rant about features which must be in before the release at the end of the week. He is questioning are those faults so bad that we really need to consume time to fix them, because we have promised some cool stuff to our customer.
Abnormal situation is work need to be done, and it's work that does not get any better with age, actually quite the opposite. It's work which generates more work. On the other hand, if we use stop the belt and fix the problem immediately it causes idling to the rest of system and the bigger the system is, the bigger the effect of idling is. So what do? I think that abnormality should always be removed as soon as it is noticed. We should always have the best understanding where we are and get back on the map quickly.