‘Out of Sight, Out of Mind’ & ‘Absence Makes the Heart Grow Fonder’ are opposing perspectives of personal reality.
Out of sight, out of mind has no personal attachment.
When something is absent, my sub-conscious mind doesn’t give it another thought.
When there is no attachment, there is no need to.
When absence makes the heart grow fonder, it is because of my attachment to whatever I am missing.
When whatever I am emotionally attached to is present, I do not need it as I already have it.
When it is absent, I start to miss it because I do not have it & I need it.
I only need emotionally what I am attached to, when it is absent from my apparent reality.
It is not my heart that is fond of what I need emotionally but my id or sub-conscious mind.
My heart is ever present, it is my awareness of my absence that disconnects me from my fondness.