Putting your foot down quickly and decisively before things get out of hand seems sensible.

decisively 是形容词 decisive 的副词形式。decisive 来自动词 decide（决定），加上后缀 -ive 变成形容词，表示"决定性的、果断的"。 decisively 作为副词，意思是"果断地、坚决地"，描述采取行动时的态度和方式。