The basic warning of this saying is that you must take care not to get too greedy in life. If you are holding a bird in the hand, you have your meal for the evening. You can take that one bird, and be well fed. If instead you let it go to pursue two birds you’ve spied in a bush, you may catch neither, and wind up hungry for the night. This proverb points out that by passing up a sure thing for a more promising possibility, you also run the risk of losing both the sure thing and the promising possibility.