You’ll be lucky
Definition 1 of 1
Pro Tip 1/3Sarcasm Alert
Often conveys sarcasm or irony rather than genuine optimism about the outcome. 
You’ll be lucky to see him before midnight, considering his punctuality!
Pro Tip 2/3Underestimation
Used to suggest someone is underestimating the difficulty of a task. 
Paint the whole house in one day? You’ll be lucky!
Pro Tip 3/3Unlikely Hopes
Indicates that the speaker thinks someone's hopes or expectations are unlikely to happen. 
You’ll be lucky if you find that rare book at any local store.