Seneca observes how people squander time on trivialities, distractions, and others' concerns while treating life as if it were inexhaustible. They postpone living authentically until some future "retirement," never recognizing that this moment—right now—is life itself.
The essay distinguishes between merely existing and truly living. Most people, Seneca argues, have long lives but don't live them—they hand over their time to anyone who asks, guarding their money carefully while freely giving away the one irreplaceable resource.
Seneca advocates living in the present, studying philosophy (which gives access to wisdom of all ages), and focusing on what truly matters. The person who lives mindfully, he suggests, experiences each day fully and thus, in an important sense, achieves immortality through quality of existence.
This essay remains startlingly relevant in our distracted, busy age.
Source
On the Shortness of Life - Seneca