פרשת מצורע תש"ל - נגעי בתים

then he that owneth the house shall come and tell the priest, saying: ‘There seemeth to me to be as it were a plague in the house.’

כנגע נראה לי בבית SOMETHING LIKE A PLAGUE HATH SHOWN ITSELF TO ME IN THE HOUSE — Even if he (the owner of the house) be a learned man and knows for sure that it is a plague he shall not decide the matter as a certainty saying, "a plague hath shown itself to me" but, “something like a plague hath shown itself to me" (Mishnah Negaim 12:5; Sifra, Metzora, Section 5 10).

...On account of proper behavior, such that a man should not say even about something that is clear to him, "[It is] certain," but rather, "[There is] a doubt." And this is what the Sages, may their memory be blessed, said (Berakhot 4a), "Teach your tongue to say, "I don't know.'"