How did humanity even manage to survive long enough reach the DAOT?

With dangerous the galaxy is, I'm always surpised that humanity was left untouched by the wars and extermination this galaxy is experencing. The planet or all life on it could have been eradicated during the War in Heaven, it could have been destroyed or taken over by the ancient Eldar empire, an Ork spore could have found its way on Earth and unleash terror, any other species could have colonized the planet for being habitable or all of humanity could have fallen to Chaos before anyone actually knew what it is.

Given the history of the galaxy, it just seems to be very dumb luck that humanity even managed to reach the Golden Age in the first place.