It's not about who is right but what is right
Don't be attached to 'your' hypothesis. Keep your ego in check.
In management consulting, we typically take a hypothesis driven approach. This means that even without getting any data or conducting any analysis, you should start developing potential hypotheses based on the given problem statement. In the following weeks of the project, as you gather data, research, investigate and analyze, you are essentially proving or disproving your long list of hypotheses to get closer to the truth.
For this to work effectively, it is important to be very objective. Don't be attached to 'your' hypothesis; the moment there is fact-based evidence or an analysis that disproves your hypothesis, immediately switch over, accept the better hypothesis and move on.
Keep your ego in check — it is less about whose idea it was and more about how, as a team, we are able to come closer to the truth.