I have that now in a project. I have two things that need t o be made where I just don't know if I'm going to get them to work well within the larger design I have in mind. I wanted to prototype them in the summer but the backend wasn't ready so I only had very small mock data served in an unrealistic way.

The only thing I can do is move them to the front of the project as much as possible, so we have the risky bits as early as possible. Once we get them to work the rest should be smooth sailing, but I'd rather fail when that time wasn't spent yet. PM agrees.