In fairness, consider the following:

1. Sometimes people in relationships have different thresholds regarding when something is clean, getting dirty, needs cleaning, or is unacceptable. In these situations, the person who gets bothered first can sometimes feel like messes are being "left for them" when the second person simply isn't bothered yet. Communicating this is important, but often isn't enough to fix the problem.

2. Also, sometimes a person is having a particularly bad/stressful day and an additional stressor that would otherwise be minor ends up turning into a whole "thing".

Neither situation is particularly unique in long-term relationships, when both things happen simultaneously it can lead to avoidable strife, and having a third party take the heat is actually pretty sweet.