This quote means that someone is saying it's the other person's loss, but they also acknowledge that it's their own loss. In simple words, they're trying to make it seem like the other person is missing out, but deep inside, they understand that they're missing out as well. It's like a two-way loss, not just one person's.
Imagine if you had a delicious cake, and you offered some to your friend. Your friend didn't want it, so you say, "It's your loss; this cake is amazing!" But in your heart, you also know that you're missing out on sharing a tasty treat with your friend. So, you're trying to act like it's only their loss, but you secretly feel sad about missing a good time together.
In life, we sometimes pretend like we're not affected by rejection, but this quote reminds us that deep down, we often feel the loss too. It's about understanding our own feelings while trying to be strong in the face of disappointment.