" you are not entitled to the fruits of action."

Tell someone that they should work without expecting anything in return ad hardly anyone would do so. It is not natural. Everyone expects some sort of outcome that one desires or expects. Without it there is no motivation to do anything.
One can do a work, or not do it, or do it differently. This how to do or not do – here one has his way. It is one’s own bidding. But one doesn’t have a choice as to how the outcome turns out to be. Why? Because, it does not depend on one alone. There will be other people involved in whatever we are doing. The time, place of action all these play a part.
We may work hard for an exam and do well in our own opinion. We expect to score high marks. Let us see the possibilities. The answer papers should properly reach the person who is evaluating. He must be in a good mood while valuating it. His must have his coffee on time in the right temperature and sugar must be just so. He should not be missing any page while reading the papers. He must be tallying the marks properly and not leave any page unturned. The marks must be entered in the registers properly. Finally it must be transferred to the computer and the mark sheet printed out right in the right name.
What should be a simple matter has so many pitfalls!
We usually encounter problems when we think the result MUST be like this. Then we start worrying as to whether it will be like we thought or not. We also worry what we should do if it does not turn out the way we expected it to. We lose sleep over these things. We also get angry with someone or something that stands between us and the result that we anxiously await. If we can do nothing about these factors we get frustrated.
On the other hand he who thinks that he would do his best and let God give him what he deems fit, has a pleasant time. At least he won’t suffer! Since his mind is at peace he would do whatever the work is in a relaxed manner which usually translates into perfection.
This is what Lord Krishna had in mind when he said, “You have right only as to what you can do. Never on the fruits.” He only meant that you are not the sole person determining the outcome. But unfortunately it has been translated wrong as the following passage shows – taken from a popular site-
[Bhagavat Gita 2:47 karmany evadhikaras te ma phalesu kadacana ma karma-phala-hetur bhur
ma te sango 'stv akarmani You have a right to perform your prescribed duty, but you are not entitled to the fruits of action. Never consider yourself to be the cause of the results of your activities, and never be attached to not doing your duty.]
This not being entitled to the fruits is the cause of all the problems associated with this verse.