You do not lose anything in Karma Yoga. Even if you do a little service to the country or to the society or to poor sick people, it brings its own advantages and benefits. The Samskaras or impressions of these good actions are indelibly imbedded in your subconscious mind. The force of these Samskaras will again propel you to do some more good actions. Sympathy, love, the spirit of patriotism and service will be developed.
Nothing is lost when the candle burns.
In agriculture you may manure and plough the land. Your efforts will be rendered futile if you do not get rain in the year. This is not the case in Nishkamya Karma Yoga. There is no uncertainty here regarding the result of any effort. Further there is not the least chance of getting harmed by practising this Karma Yoga.