No it's not that rare.
Don't kick yourself - you wouldn't have gotten that block if you were solo mining since the work your miner would be doing would be different than that issued to the pool. You can think about all the what-ifs all you want, but then life would suck...
Can you explain what that means? Genuinely curious.
Generally speaking when a miner is issued work by a pool, that work is based on the pool sending the work to a specific user. It's like there are 25 contracts out there and the pool sends out 25 contracts, and 1 user can do all 25 and return that work. The work issued to a miner can only be submitted by the miner to count for a solving block. You can't take it somewhere else and submit it (many people have thought of this idea and thought they were brilliant).
So if you are solo mining you would be working on a different project so to speak. You can read all the technical stuff if you search the forums or read the white paper.
Basically you can't turn in somebody else's homework. If you solo mine it would have been a different set of work and you probably would not have solved it.