Talking about herpes or any STI can be difficult. We aim to provide general information that covers the different situations that people may find themselves in.
The sentence you list comes from the talking to partners section of the Herpes: A Patient Guide booklet. We find having open discussions about sexual health are best but we also feel that we also need to acknowledge that in certain situations this may not be possible. The talking to partners section gives general information about how best to disclose about herpes, but we also want to acknowledge that this may not be possible all the time.
Just because someone is unable to tell their sexual partners about an STI they have had or have does not mean that they have not taken precautions in regard to transmission. We also find that most people we speak to feel it is important to them to disclose STI information to their partners.
Let us know if this does not answer your question or if you have any other questions or concerns.