The quote indicates that every little thing in life is essential and ought to not be considered given. It also recommends that time is restricted as well as useful, and also ought to be utilized sensibly. In other words, every moment is considerable and must be made use of effectively.
"The man who makes everything that leads to happiness depends upon himself, and not upon other men, has adopted the very best plan for living happily. This is the man of moderation, the man of manly character and of wisdom"