When we are fully mindful of the transience of things - an impending return home from an overseas adventure, a graduation, our child boarding the school bus for the first day of kindergarten, a close colleague changing jobs, a move to a new city - we are more likely to appreciate [be grateful for] and savor the remaining time that we do have. Although bittersweet experiences also make us sad, it is this sadness that prompts us, instead of taking it for granted, to come to appreciate the positive aspects of our vacation, colleague, or hometown; it's 'now or never.'
Sonja Lyubomirsky