That is one of the core issues that many candidates face when preparing for case interviews. Communication in case interviews and consulting work, in general, is always top-down, meaning you prioritize your key message first, then present supporting arguments for it. Everything you say needs to add value to your point or the conversation.
This is unusual since, in everyday life, people learn to communicate mostly bottom-up - the other way round.
How can you overcome this?
1. Train with an experienced case interview coach. Just one session is enough to learn the key habits of communicating properly (+ follow their exercises)
2. Learn about the cornerstones of top-down communication (e.g. signpost and number your points, lead the interviewer through your thinking process). Mino's Pyramid Principle can help here as well
3. Whatever you say, focus on answering the key question and your key message first, then follow up with supporting arguments
4. Stop talking once you have brought all your points across
Another reason why you might ramble on could be that you are not confident in your answers? I don't want to make a diagnosis from afar since we have not cased together, but I have noticed in many cases that when candidates are nervous or not confident in their abilities that they start to ramble on and
- repeat points several times using different words until stopped by the interviewer
- create endless sentences of different trains of thoughts, linking them together with 'and'
DM me if you need some more personal feedback or exercises to train this!