If there was no cut mark on the SIM card, it would have been difficult for us to properly insert it into the mobile phone.
The full form of SIM is Subscriber Identity Module or Subscriber Identification Module. It is an integrated circuit running a card operating system (COS) that securely stores the International Mobile Customer Identification (IMSI) number and its associated key. This number and key are used to identify and authenticate customers on mobile telephony devices (such as mobile phones and computers).
The SIM card used in mobile phones has a width of 25 mm, a length of 15 mm and a thickness of 0.76 mm. If you have seen the SIM card, then you must have noticed that it is cut off from one corner. The main reason for the cut mark on one corner of the SIM card is to establish the correct contact of the SIM card and the mobile phone cardholder PIN. The PIN number 1 of the SIM card should correspond to the corresponding PIN of the mobile phone. The cut mark works as a guide for the correct placement of the SIM card in the mobile phone.
If there was no cut mark on the SIM card, it would have been difficult for us to properly insert it into the mobile phone. There is a danger of inserting the SIM card from the wrong side in the mobile phone. Thus, the SIM card is cut at one corner so that we can easily identify which side of the SIM card is to be inserted in the mobile phone. Now if you see in the phone, there is a mark of putting the SIM from the right side even in the tray of the SIM card. Means there is space in the SIM tray according to the corner of the SIM card.