Men spend their lives in anticipations,—in determining to be vastly happy at some period when they have time. But the present time has one advantage over every other—it is our own. Past opportunities are gone, future have not come. We may lay in a stock of pleasures, as we would lay in a stock of wine; but if we defer the tasting of them too long, we shall find that both are soured by age.
Charles Caleb Colton

Who is the happiest of men? He who values the merits of others, and in their pleasure takes joy, even as though 'twere his own. 
Johann Wolfgang von Goethe

The chances are that you have already come to believe that happiness is unattainable. But men have attained it. And they have attained it by realising that happiness does not spring from the procuring of physical or mental pleasure, but from the development of reason and the adjustment of conduct to principles. 
from How to Live on 24 Hours a Day, by Arnold Bennett