'karmanye vadhika raste, Ma phaleshu kadachana' is famous shloka from Gita. Lord Krishna explains to Arjuna the theory of Karmas. He said believe in yourself and do your Karma (action) and success will follow you automatically. Doing Karma is in our hands only, Result is not in our hands. Below given is meaning of famous Shloka from Bhagavad Gita. 

कर्मण्ये वाधिका रस्ते मा फलेषु कदाचन।
मा कर्म फल हेतु र्भूर्मा ते सङ्गोऽस्त्व कर्मणि॥

Karmanye vadhika raste, Ma phaleshu kadachana
Ma karma phala he tur bhuh, ma te sangotsva karmanye

You have a right to “Karma” (actions) but never to any Fruits thereof. You should never be motivated by the results of your actions, nor should there be any attachment in not doing your prescribed activities.

तेरा कर्म करने में ही अधिकार है, उसके फल में नहीं ।
इसलिए तू कर्म फल में हेतु रखने वाला मत हो,
तथा तेरी अकर्म में (कर्म न करने में) भी आसक्ति न हो ।