you will be (so) lucky

/juː wɪl biː sˌəʊ lˈʌki/

/juː wɪl biː sˌoʊ lˈʌki/

used to emphasize the fact that someone's expectations or wishes are very unlikely to be fulfilled

Examples

1. You’ll be lucky!

2. Servants would be lucky to get away with a lost finger or two.

3. Catch a zebra and his family won't follow, try to ride him and you'll be lucky to keep your fingers.

4. So you would be lucky if you any of the energy you have put in at the start actually made it to the tip.