I'm still determining what sort of mantra would help me work towards goals with long time-horizons but for the time being I've got a few quotes:

It is a sobering thought that when Mozart was my age, he had been dead for two years.

It is a shame for a man to grow old without seeing the beauty and strength of which his body is capable.

The one who puts the finishing touches on their life each day is never short of time.

what would you gain from everlasting remembrance? Absolutely nothing. [So what is left worth living for? This alone: justice in thought, goodness in action, speech that cannot deceive, and a disposition glad of whatever comes, welcoming it as necessary, as familiar, as flowing from the same source and fountain as yourself.]

The future is already here — it’s just not very evenly distributed.

I have several habits that trigger sapience but I find that converting the awareness into useful action (or even thought) is difficult for me. My schedule is currently very fractured (as a full-time student) and I often have a habit of thinking "I only have {<30} minutes before {thing}, guess I can't do anything productive." As such, I've decided that whenever I think about checking my phone (a well recognized trigger) I'll assess what I want to/can accomplish before my next event (be it a class, meeting, etc).