“The pen is mightier than the sword” The exact phrasing dates to 1839, but "the idea of communication surpassing violence in efficacy had numerous predecessors" --Wikipedia
"money doesn’t grow on trees" said to warn someone to be careful how much money they spend, because there is only a limited amount --dictionary.cambridge.org
"use it or lose it" if you don't continue to practice or use an ability, you might lose that ability --Collins Dictionary
"good things come in threes" if a fortunate event has already occurred twice, a third fortunate event is likely to occur --request