以为
Meaning
以为 is a verb meaning “to think” or “to assume”, used when what the speaker thought turns out not to match reality. The real situation usually follows.
Basic structure
Subject + 以为 + … → thought that…, but actually…
Examples
她汉语说得那么好，我还以为她是中国人
马克以为今天是星期一，到了学校一看，没人来上课，才发现今天是星期天
我以为新工作比以前的好，没想到还没有以前好呢
以为 vs. 觉得
我以为今天不开会，结果还是开了
我觉得这本书很好
以为 → a mistaken assumption.
觉得 → a personal opinion, with no implication of being wrong.
以为 vs. 认为
很多专家认为这是最好的办法
认为 → a more formal “to hold the view that”; it does not imply the view is wrong.
以为 = to think or assume, mistakenly
The truth usually comes out afterwards.