Summary: She's not yours to keep; she's only yours to have right now.
This is a common phrase said on r/theredpill and for good reason.
What this phrase does is free your mind. It frees your mind of hope and expectation. The end result?
You don't break frame when she inevitably shows disinterest and you're able to keep moving forward in your life.
If utilizing this phrase properly, you've already lost her. There's nothing she can take from you. Therefore, you are non-reactive to her general attitude toward you. Hence, your frame, and furthermore, your tranquility, is unharmed by her eventual misgivings.
Ironically, this is likely to make her more attracted to you than she was previously. This is because women are attracted to strong men. A strong frame indicates a strong spirit about you. Thus, she's less likely to leave. But to reiterate, you are indifferent to either possible outcome. To you, she was already gone the day you met her.
How else might we apply this principle?
Certainly, the women in our lives no longer affect our frame, but what else in life do we allow to manipulate our emotions?
To strengthen our frame to the fullest and live a tranquil life, we must apply this rule to every area--without prejudice.
The car is not yours to keep; it's only yours to drive right now.
The job is not yours to keep; it's only yours to work at right now.
The money in your investment fund is not yours to keep; it's only yours to have right now.
Your dog is not yours to keep; he's only alive right now.
Your parents are not yours to keep; they're only alive right now.
Your life is not yours to keep; it's only yours to live right now.
Lesson learned: Be prepared to lose anything and everything without a moment's notice. This is Stoicism.
Practising stoics remind themselves daily of all of these things. Although it may seem like some sort of mind trick--it's not. It's coming to terms with reality. Everything is temporary in this world. Even, and especially--you.
"Cease to hope, and you will cease to fear." --Seneca