Some of the best sad quotes have to do with crying. Famed artist, inventor, and architect Leonardo da Vinci said, "Tears come from the heart, not from the brain." And Washington Irving, author of classics such as "Rip Van Winkle" and "The Legend of Sleepy Hollow," exclaimed, "There is a sacredness in tears. They are not the mark of weakness, but of power; they speak more eloquently than ten thousand tongues. They are the messengers of overwhelming grief, of deep contrition, and unspeakable love." In our words: don't hesitate to cry it out.

Sadness is felt by everyone, everywhere. Some people understand that without sadness, happiness wouldn't be as meaningful. As Greek singer Nana Mouskouri said: "I do believe that if you haven't learnt about sadness, you cannot appreciate happiness." Actress Alyssa Milano put it this way: "First, accept sadness. Realize that without losing, winning isn't so great." If you're trying to look on the bright side, there it is.

Almost everyone has had his or her heart broken at one time or another, and there are many sad quotes lamenting this state of being. "Everyone can have their heart broken," said actor James Marsden. "Even if you know the relationship isn't working, it's still sad. Even in a bad relationship, they're part of your life for a long time, and saying goodbye to that can be difficult." Maybe it helps to know even celebs have probably been in your shoes?

Losing a loved one is one of the hardest things we as humans have to endure. Terri Irwin, who lost her husband, Crocodile Hunter Steve Irwin, to a tragic accident, said, "Grief is never something you get over. You don't wake up one morning and say, 'I've conquered that; now I'm moving on.' It's something that walks beside you every day. And if you can learn how to manage it and honor the person that you miss, you can take something that is incredibly sad and have some form of positivity."

Many philosophers believe it is up to each of us to decide whether to feel happiness or sadness. How will you decide today? "When you wake up each morning, you can choose to be happy or choose to be sad," said billionaire entrepreneur Lynda Resnick. "Unless some terrible catastrophe has occurred the night before, it is pretty much up to you. Tomorrow morning, when the sun shines through your window, choose to make it a happy day." So -- is your glass half empty, or half full?

Humans often have a strong desire to push themselves beyond their current abilities. Former pro football player Troy Polamalu said it best: "There are times I am happy. There are times I am sad. But I always try to separate emotion from the need to reach for something stronger, deeper. And then no matter the emotion, I can reach for a stability that helps me accomplish what is the goal." In other words -- reach for the stars, even if you don't feel like getting off the couch today.

Today, the discussion around mental health is moving into the forefront, and people are working hard to dispell the stigmas surrounding it. One such stigma is that rich or successful or apparently happy people can't or shouldn't have depression. "Being sad and being depressed are two different things. Also, people going through depression don't look so, while someone sad will look sad," said Indian actress Deepika Padukone. "The most common reaction is, 'How can you be depressed? You have everything going for you. You are the supposed number one heroine and have a plush home, car, movies... What else do you want?'" Keeping this in mind can help, whether you're dealing with depression yourself or know someone who is. There is no income or age limit on depression.

Can owning a huge mansion with a swimming pool, spa, gold faucets and a bevy of servants to assist with your every need make you happy? Perhaps not. "I am convinced that material things can contribute a lot to making one's life pleasant, but, basically, if you do not have very good friends and relatives who matter to you, life will be really empty and sad, and material things cease to be important," said David Rockefeller. Rockefeller's father, John, founded the Standard Oil Company and was estimated to have $3.3 billion in personal wealth at the time of his death.

There are some remarkable people who refuse to bow to sadness. They realize it happens to everyone but do not let it ruin other things in their lives. Audrey Hepburn, actress and philanthropist, said it this way: "If my world were to cave in tomorrow, I would look back on all the pleasures, excitements and worth whilenesses I have been lucky enough to have had. Not the sadness, not my miscarriages or my father leaving home, but the joy of everything else. It will have been enough." Sometimes, remembering your own "enoughs" can help you get through.

Humans deal with sadness in different ways. Some shake it off while others sink into the ooze of despondency. American rapper Mac Miller thinks being sad is just being human. "When you feel sad, it's okay. It's not the end of the world. Everyone has those days when you doubt yourself, and when you feel like everything you do sucks, but then there's those days when you feel like Superman. It's just the balance of the world." When you're feeling down, remember the Superman feeling with come around again.