Why does John of Gaunt from the play Richard the Second act ii scene i say, "small showers last long but sudden storms are short?"

Gaunt really wants to convince his nephew, Richard the second, that he should really temper his anger and rage for war. Gaunt is alluding to Richard’s controversial war with Ireland, his vanity, his greed and his lust for admirers. He says that Richard would be well advised to slowly gain power (small showers) because waging big wars (sudden storms) are short and costly- they can be a country's undoing.