Can somebody help me to understand this quote from Shakespeare's Henry V: "A fool's bolt is soon shot"?
The allusion here, very relevantly to Henry V, is to an English bowman in battle. Obviously archers only had a limited supply of arrows (or "bolts"), and so a good, wise archer would carefully select his targets and shoot with purpose. A foolish archer would not wait and shoot at random, thereby wasting his ammunition.
This phrase has come to refer to fools in a wider sense, outside the context of the battlefield. Fools waste their time and resources in a random fashion without sense or purpose or waiting for the correct time. A fool therefore soon loses his resources or money.
This quote comes from Act III Scene 7 and occurs in a witty exchange of proverbs between Constable and Orleans. The French, in this scene, are restlessly waiting for the battle of the morn and their anxiety expresses itself in criticism of each other.