Blessings

R. Yitzchak said: "Blessing is found only in something that is hidden from the eye, as it says: 'God will command the blessing to be with you in your silos' (Devarim 28:8; ba-asamekha – 'your silos' – relates to the word samuy, hidden)." It was taught in the school of R. Yishmael: "Blessing is found only in something upon which the eye cannot gaze, as it says: 'God will command the blessing to be with you in your silos.'" The Rabbis taught: He who goes to measure (the produce in) his silo should say, 'May it be your will, Lord, our God, that you send blessing in the work of our hands.' If he began to measure, he should say, 'Blessed be the One who sends blessing to this pile.' If he measured and afterward blessed, it is a wasted prayer, because blessing is not found in something measured or counted, but only in something hidden from the eye." (Bava Metzia 42a)

From Talmud