be not supposed to be
发音大致：/biː nɑːt səˈpoʊzd tə biː/

这个短语可以拆成：

be + not supposed to + be

核心结构是：

be supposed to be ... = 应该是…… / 按理说是……
be not supposed to be ... = 不应该是…… / 按理说不应该是……

例子

He is not supposed to be here.
他不应该在这里。

This is not supposed to be difficult.
这个按理说不应该很难。

It is not supposed to be like this.
按理说不应该是这样的。

这里最容易让人困惑的是连续出现两个 be：

He is not supposed to be here.

第一个 is 是主句的 be：

He + is

第二个 be 是 to be：

supposed to + be

所以结构其实很清楚：

He is / not supposed to / be / here.

你可以把 not supposed to be 整体先记成：

“不应该是/处于……”

例如 not supposed to be here = 不应该在这里。