Evander came to Fairy Road risking his life and almost died. No, he'd have died if not for the Red fairy healing him. In return for his efforts, he cleared the trial that not even Sovereign Julius could and gained an amazing technique.
Later, he went to other partially explored regions and got the precious materials needed for his recovery. His internal injuries would recover within four to six months.
Once that happened, Evander was confident of reaching the Sovereign state. Even though the potion was mostly wasted on him, it still managed to push his talent beyond a threshold. It's an intuitive feeling that he couldn't help but trust.
That's the best future he could envision—Four months without abyssals pulling anything dangerous.
It's unrealistic. Evander would rather bet on his father Albert opening up to him than abyssals staying still.