“ Human time does not turn in a circle; it runs ahead in a straight line. That is why man cannot be happy: happiness is the longing for repetition. ”
Source: The Unbearable Lightness of Being
Similar Quotes
One swallow does not make a summer, neither does one fine day; similarly one day or brief time of happiness does not make a person entirely happy. 
Time is not a commodity that comes and goes - it just goes. Time is life. We cannot afford to squander it. 
The saddest people I've ever met in life are the ones who don't care deeply about anything at all. Passion and satisfaction go hand in hand, and without them, any happiness is only temporary, because there's nothing to make it last. 