Why do people finish speaking by saying "so"? [duplicate]

I often experience people who when they get to the end of what they were saying, they finish their sentence with the word "so" as if they are going to say something else, but they don't.

Example: "I asked him if he would fix my computer, but he said he didn't have time, so..."

I ran an "experiment" on a friend who does this all the time, and after he finished his sentence with "so," I didn't say anything. He acted as if he was done speaking, even though I waited for him to continue. I finally said, "So...what?" He said he had nothing else to say.

I thought to post this question here when I noticed the man in this video also finish his sentence with "so" but not have anything else to say:

https://www.facebook.com/video.php?v=845994225437919 (start at 1:10)

Why do people finish speaking by saying "so" when they have nothing else to say?

According to the Oxford English Dictionary, there are at least 22 different reasons to say the word so, and that doesn't include set phrases, which most likely would not apply to this end-of-sentence application.

Some of the 22 definitions might not be useful at the end of a spoken sentence. The obvious filler implication probably flows out of verbalizing an internal cause/effect thought process: I'm stalling for an opportunity to think about this before I talk.

After that, it seems that the top six terminal implications connected to the dictionary might be:

1. So... [take a moment to ponder all of the things I've just said, I'm done now]:

Referring back to something previously mentioned.

2. So... [consider the implications of all the things I've just said, I'm done now]:

And for this reason; therefore:

3. So... [and then, wait we've covered enough for one monologue, I'm done now]:

And then; as the next step:

4. So... [what do you think? I'm listening now]:

Introducing a question following on from what was said previously:

5. So... [I am resonating with your doubt, and I welcome your feedback]:

informal Why should that be considered significant?

6. So... [I'm done now]:

Introducing a concluding statement:

One might object, "Well, why doesn't he just finish the sentence?" It is true that highly articulate people complete their ideas, but in routine spoken communication, the vast majority of meaning is communicated in tone of voice and non-verbal cues. So!

www.oxforddictionaries.com

So is used to imply causation. For example:

• It was raining, so we had to cancel our picnic.
• I had never been to the city before, so I quickly got lost.
• The professor is busy right now, so you'll have to wait.

In other words, whatever follows so is a description of a result. However, sometimes the result is so easily discernible from what has already been said that there is no need to explicitly describe it. In your example, what was said means "I asked him if he would fix my computer, but he said he didn't have time, so he didn't fix my computer." However, the fact that he didn't fix the computer is obvious from the fact that he didn't have time, so it didn't need to be stated. Not stating the foregone conclusion is essentially a time-saver, and trailing off after so... is a sign that the listener can just fill in the obvious result.