happily and without feeling or showing any worry, especially when there is a reason to be worried

She blithely agreed to the contract without realizing what its consequences would be. 她愉快地同意了这份合同，没有意识到后果是什么。

A blithely optimistic 75% of the students believed that they would one day become millionaires. 75%的学生乐观地认为，他们有一天会成为百万富翁。