An hourglass (sandglass, sand timer, sand clock, egg timer) measures the passage of a few minutes or an hour of time. It has two connected vertical glass bulbs allowing a regulated trickle of material from the top to the bottom. Once the top bulb is empty, it can be inverted to begin timing again.
Our life is like an hourglass. Until the last grain of sand falls, a little part of our life is going away. As It's mentioned above, an hourglass can be inverted to begin the timing again. But life not. For the time when the last sand of life falls, life will not be able to be inverted and start everything again.
So each second may be the last for us. That's why it's so important to be ready for that time. And to be ready means to be good, respected, loved, honest, good-natured, intelligent one. a HUMAN
Every time when you look at your watch, they are reminding you about the last sand. After which it will be impossible to turn it back! Be ready - be HUMAN.