Abstract: Our most powerful telescopes have glimpsed galaxies in their early growth phase only a few billion years after the Big Bang. Surprisingly, galaxy surveys show that the most massive galaxies in the Universe were formed the earliest in cosmic time, in extreme but short-lived bursts of star-formation. I will discuss my research into the unknown astrophysics that drives, and abruptly ends, the extreme lives of massive galaxies. By integrating uniquely deep ALMA and optical/infrared imaging, I will present new insights into the growth rates and gas reservoirs of both quiescent and dusty star-forming massive galaxies during their early evolution. This research will soon take a leap forward using JWST, which will unveil the hidden astrophysics of early galaxy growth with the deepest infrared imaging and spectroscopy ever taken. I will conclude with an overview of two galaxy surveys I will co-lead during the first year of JWST and forcast how they will contribute to outstanding questions about the life cycle of massive galaxies.