Of course, it’s sensible that when making big medical or health decisions, you should take into account how much longer you’re likely to live. If the answer is either decades, or a few years, then you might reasonably make different decisions (e.g., if you’re going to live decades longer, then making lifestyle decisions to make those years happier is a reasonable choice). But for better or worse, 33% of seniors in a recent study underestimated how long they might live. Think twice, and kick those bad habits.