My own particular SMIDSY involved the driver looking past me at traffic. There were two traffic light controlled junctions, about 200 yards apart. I was at the head of the queue of traffic that started
from the first set of lights. Of course I accelerated faster than the cars, so was about 100 yards ahead of the main bulk of traffic when I came to the second junction. There was a car travelling in the opposite direction waiting to turn to his right across my lane. He stops, focuses on the "traffic" 100 yards behind me, sees he can just nip in front of them and puts his foot down, at which point my bike embeds itself in the front of his car and I get a free 50 foot flying lesson across the rest of the junction and a ride in an ambulance.

I've been SMIDSYed twice in the last couple of years in the same place. Fortunately, I wasn't knocked off, and suffered only bike damage which the drivers concerned were only too happy to pay for.

There's a T junction roundabout with three vertical lanes and two horizontal.  I'm going horizontal from right to left which is up a hill, and I'm probably doing about 10MPH.  As I come in front of the vehicles 
waiting in the three vertical lanes, the middle one drives forward into me.  No pillar,  I'm well lit, the roundabout is lit.

This is what I think happens.  The driver has a lot to concentrate on at that point, and so a lot of what he sees is what he expects to see. He's looking to the right and has seen a shape coming, but experience 
tells him that this must be well gone by now, so he drives forward still looking right, only to brake heavily when I shout.  It's as if (speculation) concentration narrows the field of real vision.

Coincidentally(?), both vehicles were BMWs, and both drivers were very concerned and couldn't understand how it had happened.  My lighting and clothing gives no excuses.