Didn't Undestand this, Please explain me

Sir told, if we can place the cows at minimum distance of 2 then we can also place them at 1 and 0, So that can be ignored.
I think We have to find the minimum distance between 2 is as large as possible so, If it is 2 then we should check for 3 because we want minimum distance is large as possible.
Please tell me If I am wrong