Can you say no to a task which is asked of you?

I do not know why the frequency in such situations Say No to manager, but at the same time try to persuade him that the thing  he requested can not be achieved

If it negotiable I would first negotiate and discuss it so that the Job will be accomplished in best term of professionalism 

From my side "Yes Always" to learn new tasks which will be useful for me in my career history.

One of the most important factor for time management is HOW to say NO.

Yes, I can.

Let me break down this question into two parts.

1. Your Manager assign you a task and you are capable of doing it

- You are bound to fulfill the requirements of your job profile and your manager can assign you all such tasks that would fulfill your job. So professionally you cannot say a NO.

2. Your Manager assign you a task and you know it cannot be done 

- In this case you should ask your manager some time to study the feasibility of the task or to understand the requirements clearly and the way it can be done. Gather information and present to your manager what are the barriers and why cannot you do it. (say you are overloaded with more tasks, your technical or specific knowledge on it etc)

 

Giving a direct answer as NO to your Manager would be inappropriate, because in my opinion, a sincere effort is mandatory after considering background checking of the given assignment. Only then, if the results are leading to failure should one update your Manager about the outcome.

If the type of work is within your job description and you are not overloaded, then unfortunately your manager is well within their rights to ask you to do any task they choose.

 

Its worth remembering, however, that one good definition of professionalism is the ability to cross the gap between what we want to do, and what we know we should do. And also be prepared to accept that at the end of the day, you get paid to do a job and that involves completing tasks given to you.

 

In my16 years of work experience in a global company, i learned do things, short, simple, and direct to the point. Which leads me to answer the question being raised as Yes, i will tell my boss right away and talk him through the pros and cons of that particular task, why is it impossible to be finished at a given amount of time, etc. In addition, I would give options on how to get it done the "the-out-of-the-box" way.

Agreed with colleagues answers

I will try to convince my manager that it cannot be done. If he insists, I will work on it. You cannot say no to your manager unless there are ethical reasons for that, it is dangerous for you, against company's regulations or illegal.

Rather then adding my answer i wish to thanks the most Senior and Respectable Personalities for giving such a great answers on this form.