One way to hold this phrase: picture someone leaning on a fence with a chance in front of them. They do not settle their feet, do not raise the sights and do not wait for the right moment. They just point and fire, because the target happens to be there. Two things follow from that one picture. The shot often misses, since nobody aimed it. And it cost the person almost nothing — no effort, no preparation, no risk. English uses the first half when real shooting is meant, and the second half when the shot is made of words.
這個說法的畫面可以想成有人靠在欄杆上，眼前剛好有個目標。他沒有站穩，沒有抬起準星，也沒有等時機。就順手一指，開一槍，因為目標剛好在那裡。從這個畫面會長出兩件事。第一，因為沒瞄準，所以常常打不中。第二，這一槍對他來說幾乎沒有成本——不費力、不用準備、也不用承擔什麼。英文講真的開槍時用前一半，講用嘴巴開的那一槍時用後一半。