Once, when I was about 10 or 11 years old, I lay down and fell asleep on a rocky island that my siblings and I often walked to during low tide. But on this day when I woke up, my siblings were gone and the tide had come in. The rocks that had served as stairs for me earlier were covered in white foamy waves.

After considering my situation, I decided to swim back. Being a competitive swimmer since the age of 7, I was not intimidated by the 400 yards back to the shore. I was, however, intimidated by the foamy water, which looked like it could toss me into a rock if I were not careful.

But I took a deep breath, plunged into the water, and began my journey. Before I knew it, I was standing by the yellow-and-blue striped umbrella and talking to my mother, who smiled at me. “Where’ve you been, honey?’’ she asked.

“On the island,’’ I said. “I had to swim back because I fell asleep when the tide came in.’’

“Oh,’’ she said. “Do you want a sandwich?’’

That was it. She was not even vaguely worried about me or impressed by my voyage.

When I think of anything I did as a kid that was a little daring or adventurous, I realize that the words, “I can’t,’’ never entered my mind. Why? Because for my parents, part of the Greatest Generation, “I can’t’’ was not in their vocabulary and so it did not become part of mine. Ask anyone raised by the Greatest Generation and they will all tell you the same thing. Our parents expected us to find our way, to be independent. Their expectations became our expectations.

And somehow, we did. We found our way because our parents showed enormous faith in us, and we felt an inner obligation to keep their faith.

And we found our way because we believed in ourselves.

Your teachers’ faith or your parents’ faith in you is not enough. You need to trust yourselves, listen to your hearts, and be true to who you really are.

If you want to have lives that matter, you have to do things that matter to you. Not to your teachers. Not to your friends. Not even to your parents. To you.

Loved ones can listen to you and guide you. But they cannot live your lives for you.

Once you discover what matters to you, go for it. Say, “I can.’’ And then, sweat the small stuff. If you don’t do the small stuff, you’ll never get the big stuff.

It starts with simple things, like homework assignments. Do them. These are your hammers, nails, screws, and saws. If you skip homework now, when you are older and building your dream, your toolbox will be empty and your dream will be flimsy.

If you want to play hockey, shoot pucks into your net every day. Shoot a million of them. If you want to play basketball, stand on the free throw line and shoot a million free throws. Singers, sing. Dancers, dance. Writers, write. Artists, draw. Put the time in.

And be brave. If the waters are foamy and the rocks threatening, take a deep breath and then pull. You’ll get there. Trust yourselves.

Our country was founded by the brave. Go to Quincy. Take the John Adams Tour, then consider the astonishing courage of John and Abigail Adams. Or go to Plymouth and take a long look at the Mayflower II. Imagine journeying on those wooden ships across the ocean. Imagine 10- and 20-foot swells, stormy nights with no land in sight. Imagine water flooding the decks, ripping the sails, splitting the wooden beams. Imagine the resilience and determination of the men and women who battled to get to America. These are our ancestors.

These people and others.

Alexander Hamilton, orphaned as a child and raised in the West Indies, is another of our amazing Founding Fathers.

I can.

Annie Sullivan, abandoned by her family, raised in an asylum, and legally blind, taught Helen Keller and became the greatest teacher in American history.

I can.

Helen Keller, deaf and blind, learned five languages, wrote books, traveled to 39 countries, graduated summa cum laude from Radcliffe, comforted thousands of soldiers and blind children, and championed the causes of the downtrodden.

I can.

You are our future America. Your generation can and will be making the decisions that will shape our country, our world. You will invent cures for diseases, create clean sources for energy, and devise safer means of transportation. You will explore space, the ocean. You will raise your own children someday, teach them to love and care for others.

You will make a difference. Your lives will matter because you will do the things that matter to you and share these things with others.

So, be brave, take a deep breath. Be a true Amer-I-CAN.

Rea Cassidy teaches seventh-grade English at Hingham Middle School. She can be reached at rcassidy@ hinghamschools.org.