Why only four digits?

I worked in electronic banking for 23 years. The protocol behind bank cards can accommodate up to eight digits. In most countries they use six digits. In the USA, and Canada they only use four.

My employer uses a four digit pin along with my electronic ID badge to open the door during off hours. My former employer (in Asia) required six digits.

Microsoft requires only four.

Why?

My bicycle combo lock has six digits. Why, because I refuse to buy one with only four digits.

The PIN on my iPhone is set to eight digits. I have no problem remembering them.

Four is easier to memorize than 6 or 8. What you find easy to memorize is not the same for everyone else.

And my library card has 9 digits.

It doesn't matter, this is how each type is set up.

You didn't learn much in those 23 years

Its only the validation of the card at an ATM that requires 4 digit -

4 digits gives a 1 in 10000 chance you will get the right one
Problem is- you only get 3 attempts to get the right one - after that the card is not returned and is cancelled
Your employer probably only requires 4 for the same reason, same with microsoft

Only having 3 attempts is pretty good security, since if you don't get it right after 3 attempts your access using that card is cancelled

Sure 6 digits would be better but only required if you DON't have an unlimited not of tries before getting the correct code

Sure the protocol may allow up to 8 digits, but banks have to balance the capabilities of ALL customers to remember the code vs the number of times they have lost money due to fraudulent use the card due to theft/loss where the user has been lucky and guessed the number
(bearing in mind, by far MOST fraudulent use has been when they have been told the number by the card holder. In this case it don't matter HOW many digits are used)

Most ATMs or other card readers will give you only 3 chances to remember and enter the correct PIN number combination for that card. If after 3 failed attempts, you will need to pay in cash or use a credit card that doesn't require a PIN. And they do this, just because you could be someone that has stolen or come into contact with someone else's card, and you are attempting to commit fraud and larceny with that card!

YEAH, those are some serious FELONIES!

Oh in answer to your question, who gives a rats hiney, how many PIN number digits are allowed/used for each transaction? Why can't you just accept that that is how it is?