It was very nice to be with laid-back people, not only because it led me to forget about unnecessary worries, but also it made me think about myself more thoroughly than before.

laid 是动词 lay 的过去分词形式，lay 本意是"放置、摆放"，在这里与 back 组成复合形容词。 back 的意思是"背部、后面"，在复合词中常表示"向后"或"返回"的状态。 laid-back 是复合形容词，字面意思是"向后靠着的"，引申为"放松的、随和的"，形容人轻松自在、不紧张的状态。