If you’re lucky you can break any encryption in under a second by pulling the key from /dev/urandom. It’s a meaningless statement without defining how lucky.
If it takes 2 years to exhaustively search the entire keyspace, you'd expect to be 50% lucky a year in, assuming the keys are evenly distributed (which is a huge assumption). If you have a lot of keys to crack and it's a feasibly short time, mean time to brute-force key recovery becomes far more interesting to you than the worst case scenario.
Which is why saying “if your lucky” isn’t helpful, but quoting time to exhaust keyspace (knowing that half the time you’ll get it in half the time) is more useful
