When you don't get it, there is still hope and you can still pursue it. When you get it and lose it, it's like hope becomes a reality but is shattered into pieces and turns into despair in an instant.
"That's fine" was Xiao Twelve's last words to Su Su.
No other scene about Xiao Twelve ever appeared in Su Su's dream. Only the scene where he pretended to be calm and said "That's okay" to her became her nightmare and her only memory.
Conception: