to advance dauntlessly in wave upon wave; describing a continuous stream of people charging forward courageously

one falls, the next follows; to step into the breach to replace fallen comrades; describes bravery and charging forward without fear of sacrifice

To have qualified successors to carry on one's work or ambitions; there is no lack of successors.

to lack qualified people to carry on a cause or legacy

to lack qualified people to carry on a task, trade, or ambition; to have no one to take over an undertaking

to lack the strength to carry on; running out of steam; failing to maintain momentum

To lack the stamina, resources, or support to sustain an effort or follow through to completion; running out of steam.