섣불리 + verb (often with negative/caution): 섣불리 판단하지 마세요
rashly, hastily, carelessly (without enough thought)
Example
상황을 잘 모르면 섣불리 판단하지 않는 게 좋아요.
If you don't know the situation well, it's better not to judge rashly.
Word parts
From the adjective 섣부르다 'clumsy, half-baked'.
Good to know
Pronounced [섣뿔리]; usually appears in warnings like 섣불리 ~지 마세요 'don't rush to ~'.