It's not a problem in novels because you have a narrator who can fill in the gaps: 'her brother said...', or you can have a character remember something that will explain to the reader why she hasn't spoken to her sister for twenty years, or whatever it is that you'd like the reader to know.
In a script, you just have the action and the dialogue to tell the story (and visual cues including props and sets). It's considered very lazy to have characters saying things like 'But you're my brother!' or 'You haven't spoken to your sister in twenty years since you had that argument about the...'
It is the job of the writer - and script editors and others who might read their work - to eliminate exposition from a script.
I have recently come to believe that it's not enough to remove exposition from scripts. We have to eliminate it from real life, too. This revelation came to me in the course of a fairly mundane conversation I was having with my daughter in the kitchen about a week ago, when I said something like, 'But you're my daughter and...' I honestly don't remember the details - it was so shocking, I have wiped it from my memory. But I stopped, mid-sentence, and saw Lauren look at me with a mixture of pity and shame as we tried to come to terms with what had happened: Exposition! When did I start talking like a very bad episode of a TV series?
I'm not alone. A couple of days ago I got off the 137 bus at the same time as a rather distressed woman of about my age who was talking on her mobile phone. 'But Mum,' she said, 'I have been at your house for two hours and I have just got on the bus. And now you want me to come back?' I felt that I needed a sticker - like one of those stickers that they used to put on fuzzy photos when you had them developed in Boots, telling you off for not doing it properly - a pre-printed sticker with 'EXPOSITION!' on it, that I could have slapped on her coat or on her mobile phone, reminding her to be more careful in future.
Alternatively, I could have discreet cards printed. Something along the lines of:
Need to eliminate it from your life?
Contact me now, ask me how.
And just hand them out, as necessary. I'm not sure whether to charge for this service or offer it for free. It's something I could probably do as a side-line when I start my emporium. I should think £50 would be about right.