Alternative form of a bad penny always turns up

Others' circumstances seem more desirable than one's own but in reality often are not.

Alternative form of the darkest hour is just before the dawn

Alternative form of the grass is always greener on the other side

It is not the tools we use that make us good, but rather how we employ them. / Upon failure, it is easier to blame the tools used rather than how they were employed.

The state, quality, or condition of being or lasting indefinitely or always; continuity; indefiniteness; eternity.