道具 are private, reflecting the
茶人's taste (→ 好み)and aspiration.
A tea devotee will not reveal to others what kind of tea utensils he has in his private collection. At a tea gathering, an event based on the principle of 一期一会, the element of suspense as to what utensils will be used is essential. (Hatakeyama Issei. Funnily, his collection ended up in a museum)