This is not a once in a 70 Day chance, if it was we all be hearing about it and everyone would be solo mining... You will need about 17,500TH to be hitting a block every 70days.
You are using a PPS method to calculate the above. Statistically it is what you would generate with the current network difficulty.
Excluding fees/cost/etc and any network diff changes, you are earning 0.00065BTC a day
If difficulty was to never rise and fall, it would take approx 9,615 days to generate 6.25BTC or approx 26 Years.
Here are some numbers and facts to drool over...
Every hash has an equal chance of hitting a block
There is approx. 175,000,000TH or 175,000,000,000,000,000,000 Hash
126TH or 126,000,000,000,000 Hash is approx 0.000072% of the over all hash rate
Remember, statistically speaking, you will never hit a block, but that doesn't mean you will not get lucky. (glitch in the Matrix)
So yes it is a once in a life time hit.
Probably Black Jack has about the best odds for the player out of any of the casino games, so long as the casino does not further undermine the odds by adding new unfair rules (or rules that worsen odds of regular blackjack)... but even with odds of maybe 1% to 2% against the player, some players believe that they can beat the odds to cause them to become 1% to 2% in their favor - mostly by attempting to play consistently with a system that maybe allows to change their bet on certain conditions (probably a kind of counting involved too, even though some players claim that they can consistently win at blackjack without counting cards).
Playing Black Jack sounds much better than the odds being described above - hence likely the reason that hardly anyone mines solo unless they have enough hashpower to hit on a fairly regular basis, maybe monthly or so.. which probably would cost quite a bit of money to get to that level of hashpower.. so yeah mining has been questionably profitable through the years as compared with just buying coins.
I suppose that if the miner cannot generate enough hashpower to attempt to hit close to 10--12 times per year, then such miner then is forced (for practical purposes) to join a pool. This post likely demonstrates part of the reason that I am not a miner.... and just a plain Jane buyer of bitcoins (or would it be a plain Joe?).
Edited: Made a few clarification and fleshing out of idea attempts.
Blackjack, like all casino (non parimutuel) games is a -EV game. (there are of course legendary exceptions to this for Blackjack in particular but that is another topic, or perhaps movie)
Mining can be a +EV endeavor.
Your example COULD be true for poker, sports betting, or horses...