Resonance

'You were right dear: she really was a Gorgon!'

Had a quick shimmy through various dictionary definitions.
Resonance is about echoes and endurance and evocation.

So, it transpires that Sylar is Nathan and Peter's brother eh? (Heroes.)
And Darth Vader is Luke and Leia's dad.
So what's the big deal? Why are so many plots peppered with familial revelations?
And just what does a reader want from an author anyway?

I'm guessing that the reader responds to things he recognises.
Or, to put it another way, that he'll not be bothered about your hero's quest if he finds nothing recognisable within it.

I asked a friend what he thought about the Heroes reveal. He wasn't bothered. I asked him what he was bothered about. He gave examples of movies that culminated in achievement and accolades - those movies in which the protag ultimately achieves his goal, typically an academic one, and receives the recognition that he has been fighting for (from his peers). My friend is an academic, about to head off to Maria country (Oxford) to create virtual bones. His family, I understand, were very hard on him as he grew up. He was designed for academia. His father has achieved great things. Hence, his views on family are tainted with none of the excitement and desire which he assigns to individual achievement.
So, it's not simply enough to provide recognisable situations; these situations need to be tailored to an intended audience.
However, family, despite being fallible as a resonant device, is usually a safe bet because it has a huge catchment area.

I was lured to a free coffee stall in the market square a few weeks ago by a girl who explained 'The boss has a new woman'. Apparently, that was the explanation for the coffee giveaway.
As a salesman, I discovered that people need an explanation. Why is this restaurant inviting me down for free grub? Why does this golf course need my custom? Why are your computers so cheap? So we would always give them a reason. It's their third birthday, or they've just redecorated, or whatever. It doesn't matter. Just a reason. People need resonance; we need to find a personal relevance, otherwise we are suspicious or indifferent. Surely, more people would be willing to empathise with the boss who has found the love of his life than would empathise with the boss who wants to entice you away from your favourite coffee shop?