Actually one can be best, it depends on how we're looking at it. If the universe of reference is narrowed down, one can be best easily. Say you're a doctor and all of a sudden at a gathering, a doctor is needed and you're the only doctor there, what then? Of course, you're the best person to help! Ok if no doctor is there, what then? What if you've done a basic course on first aid, you're the best person to help. Even if you know nothing about medicine or helping a patient, if you even take an initiative like making the person feel comfortable, calling an ambulance, you're the best person at that time because you have taken that initiative to improve the situation and help someone.
You don't have to be the best in the world to be the best, you get opportunity everyday to be the best, to make someone's life better, to make this world a better place.