The Talmud Yerushalmi (Yoma 1:1) says that if the Temple is not rebuilt in one’s life time it is as if it was destroyed in one’s lifetime.
The loss of the Temple, the Churban, is something which is not a memory, it is something we need to experience.
One way in which we experience Churban is by limiting the enjoyment of experiences. For example, when we renovate or move into a new home we may not paint it completely.
Today we will talk about this idea, the idea of zecher l’mikdash