"Do you know what damage you may cause by throwing stones with your eyes blindfold?About St. Josemaría Escrivá
"Neither do you know the harm you may cause - and at times it is very great - by letting drop uncharitable remarks that to you seem trifling, because your eyes are blinded by thoughtlessness or passion."
("The Way > Charity > Number 455"
The Way, Josemaría Escrivá)
A tip of the hat to padrejorge, on Twitter, for the heads-up on this quote.