There is a tide in the affairs of men.
Which, taken at the flood, leads on to fortune;
Omitted, all the voyage of their life
Is bound in shallows and in miseries.
On such a full sea are we now afloat,
And we must take the current when it serves,
Or lose our ventures.
William Shakespeare, Julius Caesar, Act 4, scene 3
"There’s a tide in the affairs of men," he insists; that is, power is a force that ebbs and flows in time, and one must "go with the flow.” Waiting around only allows your power to pass its crest and begin to ebb; if the opportunity is “omitted” (missed), you’ll find yourself stranded in miserable shallows.