"Unless" at the end of the sentence

Question

I was just wondering what does it mean when people use of the word "unless" at the end of the sentence. As far as I know, I only hear people say something like "Unless you work hard, you will fail." They usually use the word "unless" at the beginning of the sentence, or otherwise, use it as a conjunction, but never seen it at the end of the sentence before. (I'm not a native speaker.)

I found this in the TED talk. Could you please explain me what does it mean? (Here is the link : https://www.ted.com/talks/larry_smith_why_you_will_fail_to_have_a_great_career?language=en)

The transcript:

And that's why you're not going to have a great career. Unless. "Unless." That most evocative of all English words—"unless." But the "unless" word is also attached to that other, most terrifying phrase, "If only I had ..." "If only I had ..." If you ever have that thought ricocheting in your brain, it will hurt a lot. So, those are the many reasons why you are going to fail to have a great career. Unless—Unless.

Answer 1

Except for the unless in quotation marks, the word never appears at the end of a sentence in your example...

But it could!

In the paragraph you quote, the part that normally would follow unless has been left out. It's left to the reader's (listener's) imagination to fill it in.

This is used quite a lot:

Unless you study very hard, you will not succeed this year.

is equivalent to:

You will not succeed this year unless you study very hard.

Now look at this:

You will not succeed this year. Unless...

This leaves it to the student to decide what needs to be done in order to succeed. Studying very hard, a miracle happening, or maybe something else.

The effect is similar to the use of or else:

You'd better do as I tell you, or else...

What happens if I don't listen is not said, but I am left to imagine what the speaker might do (to me) if I don't comply!