Kurose Ross 6th Edition PN 745 R17

Question

Please explain answer of following question.

R17. What does it mean to say that a nonce is a once-in-a-lifetime value? In whose
lifetime?
Ans given ->  Once in a lifetimes means that the entity sending the nonce will never again use that value to check whether another entity is “live”.
 

Please explain the answer.

Comments

check this

https://en.wikipedia.org/wiki/Cryptographic_nonce

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Thanks :) Actually issue is that I'm not able to understand their answer ! Will surely check it to see if I can get it myself :)