Other people’s doubt is information about them, not instructions for you.

When somebody tells you it will not work, they are mostly describing the inside of their own head: what they tried, what frightened them, where they stopped. Occasionally that contains a useful detail worth keeping. It is never a measurement of your odds, because they have no access to how much work you are willing to put in.

Separate the content from the verdict this week. Ask what specifically they think goes wrong and hold on to that part. Leave the conclusion with them, since it was always a statement about their own limits.