confident that somehow I will manage为何不是thats

Question

without guides or advanced bookings,confident that somehow I will manage.为什么不是thats呢

Answer 1

这句话是个省略了成分的句子。完整的句子应当是
although without guides or advanced bookings, I am confident that somehow I will manage

尽管没有指南也没有高级的手册，但我很自信我能搞定这件事。
be confident 后面可以接从句，意思是 对.....有信心。that引导的是宾语从句。
如果用that就不通了。

供参考。

Answer 2

that 表示I will manage 的宾语 不用thats表述