goes to show, went to show

Question

‘Good God,’ said Howard for the third time, ignoring Shirley’s soft background questioning, his attention all Miles’. ‘He just dropped down dead in the car park?’
‘Yep,’ said Miles. ‘Moment I saw him it was pretty obvious there was nothing to be done.’
It was his first lie, and he turned his eyes away from his wife as he told it. She remembered his big protective arm around Mary’s shaking shoulders: He’ll be OK … he’ll be OK …
But after all, thought Samantha, giving Miles his due, how were you supposed to know one way or the other, when they were strapping on masks and shoving in needles? It had seemed as though they were trying to save Barry, and none of them had known for certain that it was no good until the young doctor had walked towards Mary at the hospital. Samantha could still see, with awful clarity, Mary’s naked, petrified face, and the expression of the bespectacled, sleek-haired young woman in the white coat: composed, yet a little wary … they showed that sort of thing on television dramas all the time, but when it actually happened …
‘Not at all,’ Miles was saying. ‘Gavin was only playing squash with him on Thursday.’
‘And he seemed all right then?’
‘Oh yeah. Thrashed Gavin.’
‘Good God. Just goes to show you, doesn’t it? Just goes to show. Hang on, Mum wants a word.’
. . . . . .
‘He’d had a bad headache for a couple of days, apparently.’
‘Ah,’ said Simon, chewing toast. ‘And he ignored it?’
‘Oh, yes, he didn’t think anything of it.’
Simon swallowed.
‘Goes to show, doesn’t it?’ he said portentously. ‘Got to watch yourself.’
. . . . . .
‘I always knew he’d pull through,’ [I believed my husband unlike the dead one above pulled through his heart attack] Shirley had said, unruffled and serene. ‘I never doubted it.’
And here he [my husband] was, as good as ever; and there was Fairbrother in the morgue. It only went to show.)
(The Casual Vacancy, by J. K. Rowling)

What does the expression, goes to show, mean? I guess, it, things that we meet, goes and just show the result when happened. What do I have to think of it?

Answer 1

The words "it only goes to show" usually introduce some pithy saying or some adage that is relevant to the facts at hand.

It only goes to show, you can't judge a book by its cover.

It only goes to show, fools rush in where angels fear to tread.

It only goes to show, a stitch in time saves nine.

When the pithy saying or the adage goes unspoken, it means the speaker believes he has no need to say anything more; he assumes the person he is speaking to will be thinking more or less what he himself is thinking. For example:

I always said that child would come to no good! His parents never disciplined him. They let him run wild. Now look where he is: in jail. It only goes to show...

The unstated adage might be something like "spare the rod, spoil the child".

Answer 2

If something "goes to show" something being talked about, it means that it provides a good example of that thing, or demonstrates what is being talked about.

I suppose it might make more sense if you shorten "goes to show" to just "shows".

In the second example, the fact that someone ignored his headache and something bad happened, this story provides a good example of how you have to "watch yourself".

In the first example, it is implied that Howard means "It just goes to show that a person can die at any time". I'm not sure why, but people often say "just goes to show" when talking about that specific thing.