It’s been one of those days.

Do you often find yourself saying that? I do. But when those words roll off my tongue, it usually has less to do with the amount of work, or the wild activity in my schedule, than the worry pecking at my brain.

When I’m fretting about business issues or family matters or household problems or health concerns, it seems to drain so much more of my energy and enthusiasm—and productivity than I spend on my usual work load.

If you’ve been working hard but accomplishing little, perhaps it’s because too much of your energy is tied up in worrying about things outside your control or things you simply aren’t controlling. Here are some thoughts about worry and the struggle it creates:

“Our fatigue is often caused not by work, but by worry, frustration and resentment.”

—Dale Carnegie, trainer

“Worry affects the circulation, the heart, the glands, the whole nervous system. I have never known a man who died from over work, but many who died from doubt.”

—Charles Horace Mayo, surgeon

“Years may wrinkle the skin, but to give up enthusiasm wrinkles the soul. Worry, fear, self-distrust bows the heart and turns the spirit back to dust.”

—Samuel Ullman, educator

“Worry is the interest paid by those who borrow trouble.”

—George Washington, President of the United States

“Most of us have had a boss somewhere along the line who ruled by terror and intentionally planted worry in the minds of everyone in the company. The person at the top can create a culture that is radioactive with worry.”

—Edward M. Hallowell, physician and anxiety expert

“A day of worry is more exhausting than a day of work.”

—Author unknown

“I believe in work, hard work and long hours of work. Men do not break down from overwork, but from worry and dissipation.”

—Charles E. Hughes, sociologist

“Yesterday I dared to struggle. Today I dare to win.”

—Bernadette Devlin, Irish political activist and member of the British Parliament