When we refer to dequeísmo, we are mentioning a serious grammatical error that, for better or worse, many people make without even realizing it. It is true that writing is not easy, but dequeism as for example, I thought I was at home, is a practice that happens relatively frequently. The rule that you must follow in order not to be mistaken is to know what type of sentence it is and see if it is subordinate or if it is, for example, a verb. Examples of Dequeism are this depends on what she wants, instead of just using what, or, he heard she was coming. Therefore, to avoid future examples of dequeism It is important to know how to make proper use of expressions, avoiding the use of, of that and other similar ones such as la que, con la que or similar. However, you must be careful because there are situations such as the woman I was talking about, in which the use of the expression that is correct.