From a BP chat with Steven Goldman (who's fighting cancer):

Trieu (Cambridge, MA): I think everyone should always make decisions on a mortality basis. If only we had the strength to do so.

Steven Goldman: Nah... It's a sad way to live. What makes life tolerable is our ability to forget where it's all heading and just lose ourselves in the moment(s).

Interesting answer. The stock answer is to live each day as if it's your last, but I suspect Goldman is right in that it would be exhausting and impractical. Instead of carpe diem, perhaps carpe annum is the more practical time period.