Must the first letter of people name capitalized on any occasion?
Michael Scofield, is a person name. Why I hear sometimes people call him Michael while sometimes call him Scofield?
When I first read your question, I thought, "Are you sure people call him Scofield? Perhaps they refer to him as Scofield."
Here is the distinction: Calling someone a name means you are using that name to address the person directly.
Hey, Scofield! Didn't you hear me? I asked you to come over here.
Referring to someone by a name means you are referencing the person indirectly.
Scofield earned a degree in civil engineering from Loyola University.
In most day-to-day conversations, we call people by their first names, although in certain situations, we may refer to people by their last. That said, there are certain places where it's normal for people (even friends) to address each other by their last names. (These tend to be areas with strong authority figures, such as in the military.)
Because Michael Scofield is the name of a fictional prisoner, however, I wouldn't be surprised if you've heard him called Scofield. I think it would be very common for prison guards to use last names when calling to or referring to prisoners.
In most other contexts, though, such as a business meeting, you would call him either by his first name, or (if the situation demanded more politeness) you would use Mr. Scofield, not Scofield.
Yes, we always capitalize the first letter of a name. There are a very few exceptions, like the poet e e cummings, or the rock band "moe." or the rock band "fIREHOSE", but those are considered specific styles for artistic purposes, not a general rule.
Usually, we call people by their first name if we're being informal or we know the person well, and by their last name if we're speaking more formally or we don't personally know them. Exceptions are if the person is publicly known by only one name (like Charo, Adele, or Oprah) or they're royalty (like Queen Elizabeth). And sometimes individuals just prefer to go by a last name, or we use the last name if the first name is ambiguous - at my last job, there were four people in our group named "Mike", so we called them by their last names.
The first letter is usually always capitalized in names, and that convention is used to signify that it is the proper noun of something.
Using surnames to address someone, without a title, is a time honoured custom in British public schools. The reason is that surnames tend to be more unique than given names in western culture, so ambiguity can be avoided. Use, in this way, is usually defined by the custom and tradition of the group but is absolutely appropriate.