people only see what they are prepared to see 为什么有个are,而不是they prepared to see?

问题描述:

people only see what they are prepared to see 为什么有个are,而不是they prepared to see?
如果就语法来说的话“people only see what they prepared to see”有没有错?还是只是表达的意思不一样而已?

be prepared to do sth 准备好做某事
要是把be(are)去掉就只能理解成过去式了