The luminosity of a star is highly sensitive to the gravitational constant, changing to the seventh power of that value.

“what you find is that the luminosity of a star is extremely sensitive to the value of newton's gravitational constant to the seventh power”

Changing the strength of gravity too much would likely result in a universe where stars and galaxies fail to form or everything collapses into black holes, precluding life.

“broadly speaking if gravity were too strong all else being equal then things would collapse ultimately into black holes very quickly so the early universe would not have formed extended structures like galaxies and solar systems”