Agnosco Momento
I wish I'd appreciated the value of time much earlier in life (I'm now in my 50's).
There really is a gradual mental shift that takes place as you age. When you're young, your vision is incredibly myopic. Old age seems so very far away that although you know you're mortal, time seems so vast and full. We waste so much time when we're young, thinking we have so much leeway. It's only when you're much older that you begin to realize, this is not the case. Assuming an average age of 85, those years can go by very quickly.
Teachers and parents may tell you a little about this. I remember that speech about "squandering your time." But it didn't feel real. I expect that there's no easy way to get through to the young mind to appreciate it, because if there was we'd all know about it.
So I spent most of my life being in a mindset of always looking forward to the next thing, and not really being truly happy with who I already was, the people I know, and the things I have. I had the misconception in my mind that if you don't keep looking ahead, you're not driven to get anywhere. And well, that's not really true. Maybe you won't get there quite as fast, but you will get somewhere. Do we ever really think about what we'd do after we achieved some life long ambition?
There is that well known saying "Carpe Diem," seizing the day. But that implies exploitation, that you have to try to do everything you possibly can in one day. But I think there's a better phrase, "Agnosco Momento". Appreciate the moment. Be cognizant of the time, notice all of it. Take it all in. That's living. Not racing to some destination, but living in the moment.