All purposes served by a small well can at once be served by a great reservoir of water. Similarly, all purposes of the Vedas can be served to one who knows the purpose behind them. (46) [2.46]
You have a right to perform your prescribed duty, but you are not entitled to the fruits of action. Never consider yourself the cause of the results of your activities, and never be attached to not doing your duty.
One who is attached to the results of his work is also the cause of the action. Thus, he is the enjoyer or sufferer of the results of such actions. (47) [2.47]
Out of ignorance only, less intelligent persons try to adjust to the situation by fruitive activities, thinking that the resultant actions will make them happy. They do not know that no kind of material body anywhere within the universe can give life without miseries. (51) 
When your intelligence has passed out of the dense forest of delusion, you shall become indifferent to all that has been heard and all that is to be heard. (52)  It is said that a fool is undiscovered as long as he does not speak, and certainly a well-dressed fool cannot be identified unless he speaks, but as soon as he speaks, he reveals himself at once. (54) 
One who is not disturbed in mind even amidst the threefold miseries or elated when there is happiness, and who is free from attachment, fear and anger, is called sage of steady mind.
He accepts all miseries as the mercy of the Lord, thinking himself only worthy of more trouble due to his past misdeeds; and he sees that his miseries, by the grace of the Lord, are minimized to the lowest. Similarly, when he is happy, he gives credit to the Lord, thinking himself unworthy of the happiness. Consequently, he is not at all angry even when his attempts are unsuccessful. Success or no success, a Krishna conscious person is always steady in his determination. (56) 
As long as one is in the material world there is always the possibility of good and evil because this world is full of duality. (57)
SOURCE – Book – BHAGAVAD GITA AS IT IS