If only that invention wasn't supposed to be strapped to the same part of the person's anatomy as the jetpack, with the result being that no practically working implementation combining the two exists...
It's also not the solved problem your snark implied. I mean, someone's been working on it for decades and his solution is fly over water as much as possible!
(As other posters have alluded to, parachutes won't save you at low altitudes. In the mean time, it's further weight on your back on a device which is already difficult to control, and not really optimal for releasing next to jets of hot kerosene either)
Tens of person-years of work is not as much investment as you are implying in the context of manned heavier-than-air flight. Boeing spends ten person-years on developing flight every 40 minutes on average. Since you wrote your comment 4 hours ago Boeing has spent about 60 person-years on developing flight.
