What I learned from an empty store - baseline expectations

 There is a blog post that talks about how "keeping your head on a swivel" is bad advice. I won't go into all the details here, but the idea was that being on high alert all the time doesn't work.  A better view is to see what is different or out of place.  

This was highlighted very clearly about20 years ago. 
I was coming home from work one day and stopped at the BP in Bethel Park at the intersection of Rt88 and Clifton park rd, for those that are around Pittsburgh. 

So I park the car and walk into the store and it's empty. 
I mean, no one is in the store. 
Here's the thing - this story is normally very busy, customer coming and going, getting gas, several at the counter. 
No one, not even the person behind the counter. 
I instantly went into on guard. 
What does a usually busy gas station that is now empty mean ? 
Robbery with people being held in the back. 
I paused by the front door, ready to exit if needed but scanning everywhere. 
After about 5 seconds a store clerk came out from the back room. 
I asked " Everything all right? Not usually this empty..." No problem, just a slow afternoon.
 So you see, it wasn't the baseline, what is normal that was the issue. It was the deviation from that baseline.  
Busy to empty. 
Another example is someone acting out of character - a normally morose, grumpy co worker suddenly all bring and cheerful talking about how things are going to be different after today. 
The stingy, money hoarder suddenly giving away money. 
It's almost like saying " People aren't supposed to ______"  Be here, be there, be this happy, act in such a way.