If you can’t think of the last time it’s happened there are two feasible reasons. The first is that you’re losing your mind and therein your ability to remember simple things. The second is that it’s been so long perhaps it’s time to try again. The third is that you’re doing it right now and on some seriously mind-altering drugs that are confusing the hell out of you. Given that none of the above are particularly likely, perhaps it’s time for a brief review.