I am curious about how the INSTEAD OF clause works in the TRIGGER statement.

If I had a table in which I were trying to prevent duplicates on a name field, and were using an INSTEAD OF clause in it for INSERT, UPDATE, and I was then doing for example, an INSERT statement to set off the trigger, does this mean that the INSERT statement would never actually be used at all, and that everything I'd need to do would have to be contained within the Trigger itself?