internet - Can someone explain to me exactly why it's bad to use NS name that is a subdomain for the domain that NS is for

Reading a book and it states that you should not register
nameserver names such as ns1.example.com for the domain
example.com as you'll create a catch-22 situation when looking up ns1.example.com etc.
I know what a catch-22 is, but I just don't see how this fits in.

At which stage does this occur exactly, when internet central directory queries whois records
for that domain to find nameserver ip ?

excerpt from "The difinitive guide to CentOS (APress)"

Caution As you can imagine, telling the world that the primary DNS
server for example.org is dns0. example.org has some issues. Mainly,
this has you running around in circles because you’ve created a
catch-22 situation. You cannot look up dns0.example.org because to do
so you need to ask dns0. example.org. Now, as long as you have name
servers in another domain, this will still work, but it’s clearly a

bad idea. Stay away from this one, and if you have to, use a so-called
glue record that defines dns0.example.org in the parent .org zone to
solve the issue.

Answer

It's simply not true to say that doesn't work, or causes problems. For example, on my main domain:

[madhatta@www tmp]$ whois teaparty.net
[Querying whois.verisign-grs.com]
[Redirected to whois.tucows.com]

[Querying whois.tucows.com]
[whois.tucows.com]
[...]
 Domain servers in listed order:
    NS.TEAPARTY.NET   193.219.118.102
    NS2.TEAPARTY.NET   78.46.204.154
[...]

which works just fine. The technical elements that makes this work are the glue records, which you can read about at the link above, and elsewhere.