Broader equities have been volatile this year, but that's par for the course. The fact that the stock market will sometimes go through erratic periods is not a good reason not to invest. However, times like these might help remind us that some corporations are more resilient than others. Among the most resilient are longtime dividend payers with excellent underlying businesses and strong outlooks.That description fits Zoetis (ZTS 0.33%) and Abbott Laboratories (ABT -1.17%), two giants in the healthcare sect ...