The above quote comes from aphorist Mason Cooley, who reminds us that the only cure for inactivity is action. Regret has its purpose in the scope of human emotion, however sitting around feeling guilty because you haven't done anything all day (or all year) doesn't accomplish anything.
For most of us, that moment or realisation feels heavy. At 7pm on Saturday, when we realise we've spent the entire day watching TV, the list of things we need to accomplish feels like a crushing weight. Yet, that first thought of "I haven't done what I need to do" should be all the nudging we need to get moving. Otherwise, we're just perpetuating the problem.
"Regret for wasted time is more wasted time." [The Quotations Page]