I have quoted this many times but it appears that neither it nor T. Roosevelts admonition for the Strenuous Life has much affect on the faint hearted. However it is always worth another try.

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.

Julius Caesar Act 4, scene 3, 218–224