Sforno on Numbers 23:13/ספורנו על במדבר כ״ג:י״ג

1אשר תראנו משם, so that you can focus on them with your evil eye.

2אפס קצהו תראה וכלו לא תראה, do not try and look at all of them simultaneously, because if you will do you will not even achieve part of your objective. Compare the meaning of the word כלו, כלה in Jeremiah 46,28 כי אעשה כלה בכל הגויים ..ואותך לא אעשה כלה, “whereas I will make an end to all the nations, I will not utterly destroy you.” [seeing that the Jewish people have been assured that they will never be totally annihilated, do not try and do what is an exercise in futility, but try and make your curse effective against part of them. Ed.]