Since even before the NBA was the NBA, the Boston Celtics have been living, breathing evidence that hard work (and a bit of luck) can turn even the worst starts around.
In fact, they started doing so in just their second year of existence, somehow making the postseason after starting 11-9. Probably the fact that the league, the Basketball Association of America (BAA) only had eight teams in it had something to do with it, but even Boston has been outdone - and handily - since.