Topping up Cepas Card

I saw something funny when i was at Novena MRT. I had some problem with my Ezlink card and approached the control station for help. Pasted on the control station service counter's window, there is this notice...

For Topping up Cepas Card

Give us your Cepas Card

not 

the Whole Wallet

I was amused and ask the staff at the control station, why place such notice? The friendly staffs told me that, it happen many many times before so they have no choice but to place this notice.. There are some customes who give them the whole wallet even argue with the staff when told to just give Cepas card not the whole wallet..

Imagine when ask by the traffic police for your driving license, pass him the whole wallet.. see the reaction of the traffic police.. or when you go to the bank, pass the whole wallet to the teller and say, i want to withdraw $50... When ask for the bill in a restaurant, you pass the whole wallet to the waiter, you see what happen when they return you the wallet.. ??

Well its common sense to pass someone the particular document one required and not the whole wallet or bag..