‘Wasn’t that frustrating?’ already suggests an answer. ‘What was that like for you?’ leaves more room for the other person’s experience. The difference is small, but it changes who defines the story.
A useful follow-up question builds on something the person actually said. If they mention that a meeting changed their plans, you might ask: ‘Which part of the week did it affect?’ That is more attentive than switching immediately to a similar experience of your own.
Ask one question at a time when the subject needs thought. A series of questions can make the person decide which to answer and which to ignore.
You can also make a question optional: ‘If you want to talk about it, what happened next?’ This matters when the topic is personal and the other person may not want to provide more detail.
Follow-up questions do not need to uncover everything. Sometimes the useful next step is an acknowledgment or a pause. Curiosity becomes considerate when it respects the other person’s choice about how much to share.
Before asking your next question, check whether it follows their message or advances your own theory. Let the answer teach you something you did not already decide.