Communicating doubt and changing course can sometimes be a signal of self-awareness and maturity.  But for career development, projecting confidence and consistency is the better plan.

Internal State:

I don't know what we should do with my life - it is a judgment call, and I don't have the experience or data to make a strong recommendation.  Thus, I'll choose the option that looks most attractive in the moment.

External (Manager's) Need:

 Clear signal of what you want to do.

Source of Conflict:

You're setting the wrong standard.  Uncertainty is expected.  If you get to 100% confidence, then you've wasted a bunch of time. 

Resolution:

Your manager can't read your mind, and constant oscillations will lead to immobilization, eliminating your strongest advocate in your organization.

Make a choice, based on a simple consistent narrative and stick with it.  Don't go chasing shiny objects.*  Devote yourself to reaching clarity.  Only when you reach a significant change in your understanding, and have found a simple, linear way to communicate it should you ask your manager to change course.

* Be careful pursuing opportunities inconsistent with your career path narrative.  The groundwork within your organization hasn't been laid for such a change, and your manager may become immobilized.  If you don't get the position, you will need to work to re-establish your career narrative.