Leave the donuts. Take the gun.
That’s what I like about this site. I learn that the dye packs actually aren’t easily discernible but my favorite answer was “let go of the big pink box”. 
That’s assuming that a drug addict is going to keep robbing people until he/she gets to $4000. If they need $100 to get their fix, any other method is going to be more successful.
But as the OP suggests, criminals aren’t likely to make that calculation. The risk of physical confrontation is much higher in a mugging, as is the likelihood that others will intervene to stop you. Banks are where the money is, and getting caught after two days might qualify as a success if your only goal is to get your next fix.
One of my brothers, a LEO, who used to be specialized in serious crimes, indeed said that most crimes are trivially easy to solve and most criminals idiots. The example he gave then was a murderer who left a ticket with his name on it at the crime scene, and subsequently let them enter his place with a pile of blood tainted clothes in plain view.
While I was staying at his place, I once read a witness interrogation report laying around. A body had been discovered and some young teens had correctly assumed that 1)that their very recently missing friend had in fact been murdered 2) that the body was his 3) that the father of another friend was the murderer. Even before the body had been found, the kids had inquired themselves (following their “suspect” around, etc…) and essentially solved the murder by themselves, backed with evidences. I thought a movie made following this “script’” wouldn’t appear believable. The worst thing was that the murder had been commited merely to steal € 1000 worth of cannabis.
This last point often makes me shake my head. Criminals risk a lot for almost nothing, even when they have otherwise a decent place in society (as opposed to drug addicts or whatever). I see such examples all the time in local news. For instance the head of a post office (that doubled as a bank) organizing the robbery of her own workplace. Total loot about € 10 000-20 000 (to be divided between whatever number of accomplices). I wouldn’t know how she could make, but risking even only losing her job over such a trivial amount doesn’t make sense. Let alone having to face serious criminal charges. And she didn’t even had the excuse of not knowing how much money could be stolen.
Oh…and the example given to me by a friend who does shop security. He recently caught a thief stealing some random stuff. Once alone with culprit, she (the culprit) showed off her police card trying to pressure him into releasing her. Moron. You realize you’re going to lose your job over a pair of pants or whatever it is you stole? My friend had to spell it for her. He let her go after merely paying the stuff (maybe I would have had pity too, but having LEOs who steal and try to intimidate people doesn’t necessarily seem a good idea to me).
So, yes, apparently, from the murderer to the shoplifter, most criminals seem to not be that bright, not able to weight the pros and cons (even within the frame of a criminal mindset), and there’s no reason to assume they aren’t at least as ignorant as the general population.
Because, being a bank, they need to have at least some cash around? $ 4 0000 seems a very low amount to me.
One of the best OP titles, ever!
Why not keep a trivial few hundred dollars at the till, and have the rest in a back room vault?
Mr. Smith wants to withdraw $4,000, then you need to go to the back and get it.
Robber wants to steal your money, you give him $200. He demands more, and you need to go get it: whereby you push the silent alarm button on the way. If he hops over the counter and follows you then one of your colleagues can push the alarm button.
What’s wrong with this scenario?
$4000 is basically just 4 to 8 people asking for cash from the teller. If you want less than that you got the the ATM.
A pack of $20 bills is 2,000
A pack of $10 bills is 1,000
A pack of $5 bills is 500
A Pack of $1 bills is 100
Just by having the minimum of each denomination, you have 3,600 in the drawer. (not counting coins).
And keep in mind, a teller can’t access the vault. At my bank no one could ever go into the vault alone, actually. So you’re saying every time a teller needs cash, you have to take a them and a manager, off duty, just to get more cash? (the teller has to come because they have to sign for the money and personally insure the contents of their drawer.) Cash they’re going to use up in a couple of hours? Bank robberies are actually quite rare, and the perp is almost always caught. Why inconvenience your customers that way?
:::hijack::: Advice: If you don’t want to see some slashfic, don’t Google the Coraline quote “I’ve never been inside the Pink Palace”. ::::shudders::::: :eek:
Makes sense. Thanks.
Regarding the amount stolen, a robber can also ask for the money from more than one teller.