The base rates for successful ideas are very low. Industry-wide, among the strongest product cultures, it might be as high as 30% of ideas that deliver the intended value.
If you aren't in one of the best product cultures in the world, I suggest you set a baseline assumption of 10%.
Establishing world-class discovery practices can 3X your expected value (EV) by bringing your percentages up to world class levels (10 → 30%).