Why is UDP unreliable?

Related questions

1. What is a file checksum?
2. How many errors can CRC detect?
3. Where is checksum used?
4. What is checksum in transport layer?
5. What is the difference between a checksum and a hash?
6. Does TCP use checksum?
7. What is the 3 way handshake?
8. Why do we put 1's complement of the calculated checksum in the checksum field?
9. How TCP checksum is calculated?
10. Is TCP checksum necessary or could TCP allow IP to checksum the data?

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23. #reliable