Fetching details from the dictionary...
before one's own eyes; from under one's very nose; without doing anything; without resistance; helplessly; negligently; knowingly
チャンスをみすみす逃してしまった。
I let the chance slip away right before my eyes.
みすみす失敗するのを見ていられない。
I cannot bear to watch the failure happen helplessly.
大事なものをみすみす手放すのか。
Are you going to let go of something important just like that?