These failed memories have largely become part of Ian's current character and instincts—now, to avoid failure, Ian is perfect from beginning to end. He would never make those 'failed choices'; simply following his heart allows him to tread the correct path.
Moreover, Ian's past choices have helped the current Ian to navigate many extreme possibilities.
For instance, slaughtering the entire world, gathering the power of the Whole Terra to try to break through the Sixth Echelon... Although it's unclear whether it's an optimized version of the Deceased Monarch or the Heart of Terra, this path is not feasible.
Another example, the Perpetual Motion Machine is not in the material world, blowing up Terra won't obtain it—this is also a very straightforward lesson, at least for now, Ian has set aside the idea of blowing up Terra, sparing the entire planet from disaster.
Finally, there's the second prince.
