We all tend to view the world through the prism of our own prejudices. What this means for a writer is that producers, script editors, actors and even your agent will react more positively to characters who correspond to their lives and experiences.
Characters who’ve done what they’ve done, have what they have, and want what they want will simply seem more “real” than characters with whom they have nothing in common. That sometimes means we have to analyze our own unconscious decisions to see if we’ve made the most relatable choices for our characters.
Writers who don’t get on with their relatives, or who’ve grown up as orphans, tend to write characters with few relatives, whether that serves the plot or not. Writers who’ve fared badly in relationships write characters who avoid romance, or who have unsympathetic romantic partners.
And if that’s what’s required to make your story work – brilliant. Go for it.
But if it isn’t, bear in mind – the further your character is from “normal” life (and yes, I hate that word as much as you do), the harder it will be for the reader to empathize with them. They won’t be aware exactly what’s causing them to lose empathy, to feel your characters are unsympathetic or unreal – but it will still affect their judgment of your script.
So, unless it’s an important part of your story that your character is isolated, alone, or disenfranchised, integrate them as far you can into “average” human society. Give them a wife/husband or boyfriend/girlfriend. Give them children, or state that they’d like to have kids one day. Give them parents, aunts, uncles, cousins, siblings. Give them a job and a widescreen TV and a kick-arse stereo system and holidays in wherever’s the ‘in’ place to go this year.
You’ll hardly even notice the difference – but anyone reading your script will suddenly find themselves more drawn to the characters than they were before…