Because SIM cards are electronic, here is a small list of what can cause them to fail:
- Electric shock from the battery of the device they are supposed to go in.
- Static electricity.
- Corrosion if exposed to excessive humidity.
- Bad handling, like being bent.
- Age: degradation of the materials they are made of.
Just treat your sim card with care, and your phone will have internet if the bill is paid, and the sim card is inserted correctly.