Your duties will change according to your stage and role in life, your temperament and the profession or work you take up. If you decide to be a doctor, remain steadfast in your duties as a doctor for as long as you play that role. When your role changes, fulfil your new duties and responsibilities. Whatever role you take up, fulfil it without reservation, no matter how ordinary that role may be.
Many of the big names in any field today started their careers in very humble positions, as clerks, waiters, assistants, junior staff and so forth. But they played these roles well, no matter how small the part, and grew from there.
Do the small jobs as well as you can: that is how you will progress up the ladder of success.
Whether you know your purpose in life or not, do whatever work is at hand uncompromisingly, to the best of your ability. When your mind is thus freed from the anxiety and agitation caused by likes and dislikes, it becomes a channel for the power of efficiency and you will excel in all work you undertake.