As I was shifitng to new location, I just came across "Bhagavadgeetha As It Is by A.C.Bhaktivedanta Swami Prabhupada" a classic of world literature, in my collection of books.
I had skimmed through it long back.I still remember the line that has the spirit/essence of the whole book for me.
"You have a right to perform your prescribed action,but you are not entitled to the fruits of your action.
Never consider yourself the cause of the results your activities,and never be associated to not doing your duty."
(Translated from Sanskrit:-"Karmanye Vadhikaraste Ma Phaleshu Kadachana,
Ma Karma Phala Hetur Bhurmatey Sangostva Akarmani")
How simple and how relevant even today.I think if Bhagavadgeetha is universally renowned as the jewel of India's spiritual wisdom , its because of Karma Yoga.You rarely find spiritual books/Gurus laying emphasis on doing your work.
Thats exactly what Krishna says here.Always do your best without expecting the results and you will be happy.
Some short explanations
All about Krishna