Epizeuxis is the emphatic repetition of a word, with no other words in between. It's used to highlight a strong emotional state or to emphasize a point dramatically.

An iconic example is from Shakespeare's ‘King Lear': ‘Never, never, never, never, never!' This repetition conveys deep despair and emphasis on Lear's tragic situation.

How do you get to Carnegie Hall? Practice. Practice. Practice.
What's the secret to success? Location. Location. Location.
What are the three reasons most businesses close their doors during their first two years? Failure to . Failure to . Failure to .

You might hear it in speeches or advertisements to drive a point home:

‘Now, now, now is the to act!'