Found this article on special assessments on another HOA website. You need to sign up to access the full article (and maybe pay a fee), but the short version makes an interesting point about allowing time for owners to process the idea of a special assessment, comparing it to the stages of grief.
Having an effective Reserves Policy can help to eliminate the need for special assessments (and avoid the angst for owners altogether). See our "Best Financial Practices" guidelines for ways to ensure your financial stability and avoid the stress involved in special assessments.