Again, using the S7 as an example, at the current difficulty, you would expect to find a block after hashing for 161561576.41029279010546 seconds. Convert that into days and you'll see an S7 would expect to take 1869.92565289690729 days to find a block.
I think I have a better view now!
But when we say "an S7 would expect to take 1869.92565289690729 days to find a block" , I suppose it is an average ? in solo mining, it could be in a minute or never , right?