Let a man not cling to the pleasant

Mā piyehi samāgañchi, appiyehi kudācanaṃ;

Piyānaṃ adassanaṃ dukkhaṃ, appiyānañca dassanaṃ.

Let a man not cling to the pleasant, much less to the unpleasant. Separation from the loved und being with the unloved both bring suffering.

Dhammapada, 210.