Karma Yoga. New York, 1896. Complete Works, 1: 115.

There are only two ways out of this complex world-machine: one is to
give up all concern with the machine, to let it go, and to stand
aside, and give up our desires. That is very easy to say, but is
almost impossible to do. I do not know whether in twenty millions of
people even one can do that. The other way is to plunge into the world
and learn the secret of work, and that is the way of Karma Yoga.

Karma Yoga. New York, 1896. Complete Works, 1: 115.