before one's eyes; right in front of one; helplessly
Describes a situation where something undesirable happens right in front of you while you are unable or unwilling to stop it. Often used with verbs like 逃す, 見逃す, 負ける, or 失う. Carries a nuance of frustration or regret.
I let the chance slip away right before my eyes.
He was helplessly defeated by the enemy right in front of him.
I let a golden opportunity slip right before my eyes.
Even though we had the ability, we lost to our opponent right before our eyes.
He lost his fortune right before his eyes, unable to do anything about it.