My favorite philosopher, Bertrand Russell, wrote this in his wonderful
book The Conquest of Happiness:

Chapter 10: Is Happiness Still Possible?

[T]he most intelligent young people in Western countries tend to have
that kind of unhappiness that comes of finding no adequate employment
for their best talents....Cynicism such as one finds very frequently among 
the most highly educated young men and women of the West results from
the combination of comfort with powerlessness....

The pleasure of work is open to anyone who can develop some specialized
skill, provided that he can get satisfaction from the exercise of his
skill without demanding universal applause....those whose interest in
any such cause is genuine are provided with an occupation for their
leisure hours and a complete antidote to the feeling that life is
empty....

Chapter 11: Zest

Perhaps the best way to understand what is meant by zest will be to
consider the different ways in which men behave when they sit down to a
meal. There are those to whom a meal is merely a bore; no matter
how excellent the food may be, they feel that it is uninteresting. They have
had excellent food before, probably at almost every meal they have
eaten. They have never known what it was to go without a meal until
hunger became a raging passion, but have come to regard meals as merely
conventional occurrences, dictated by the fashions of the society in
which they live. Like everything else, meals are tiresome, but it is no
use to make a fuss, because nothing else will be less tiresome. 

Then there are the invalids who eat from a sense of duty, because
the doctor has told them that it is necessary to take a little nourishment  
in order to keep up their strength. 

Then there are the epicures, who start hopefully, but find that
nothing has been quite so well cooked as it ought to have been. 

Then there are the gormandizers, who fall upon their food with
eager rapacity, eat too much, and grow plethoric and stertorous. 

Finally there are those who begin with a sound appetite, are glad of
their food, eat until they have had enough, and then stop. The
happy man corresponds to the last of our eaters. Those who are
set down before the feast of life have similar attitudes towards the  
good things which it offers....What hunger is in relation to food, zest
is in relation to life.

The more things a man is interested in, the more opportunities of
happiness he has and the less he is at the mercy of fate, since if he
loses one thing he can fall back upon another....

[E]vents only become experiences through the interest that we take in
them: if they do not interest us, we are making nothing of them....Life
could never be boring to a man to whom casual objects offered such a
wealth of interest.