Of course both of them are right: the first one is talking about lazy testers and the second one - about I-will-do-my-best testers. But I think that actually there is point to decide should you blame yourself for missed bugs or not. And the answers depends on personal nature - does blaming helps you to be more attentive next time? If does - so let it be excuses.
As for me, excuses are more productive than reasons: I'll better believe in that I am capable to do better testing, than that I did my best and there are missed bugs in the result. So if you consider for example lack of time for regression testing as excuse, you will try to use your time more productively.