Own and use a really good telescope and train it at the stars.

LSD.

Travel. As much as possible. Experience how the rest of the world lives.

Watching the birth of your first child.

International Travel should top the list. I know so many adults in their 50s and 60s who've never been to the UK, for example, or Europe or China. I've been to all 3 and I have to say it opens your eyes and your heart in ways that you can't get from reading a book, watching a movie.

I did disaster relief with the Red Cross in NC after Hurricane Matthew. It was one of the most meaningful things I have ever done. Definitely life-altering

Witness, or help with, the birth of another living thing. Preferably a child. The best? Your child.

But helping to bring a life - any life - into the world is life altering.

SCUBA diving in a clear, warm ocean on an active reef; alternatively with either some playful interactive manatee, dolphins, or a manta ray.

(I am a NAUI Divemaster and used to co-own a dive store; I've been fortunate enough to have experienced all three)

Love for an animal.

Learn a new language or try....

Young adults should attend the death of a loved one. At the age of 27 I held my mother's hand as she died of cancer. I had a new perspective on my life.....and my petty concerns and fears.

Immerse themselves in a different culture.

Risking life and limb for a physical thrill...and coming through unscathed, of course!

everyone is different. there is no list that applies to all. some people should get married. some definitely should not. the same goes for having kids. the same goes for almost everything!

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Should? How about an infusion of incredible wealth? Can I wish that for everyone? I know. How we need to downplay that. If there is any life-altering thing everyone SHOULD experience, other than falling in love with someone who loves you back, it is the unexpected infusion of incredible wealth.

And I am not 100% certain about that love thing.

Have a baby! Unless you hate kids.

Watching your child achieve their dream. Nothing brings you more joy than seeing untempered, unbridled, pure joy in your child (juvenile or adult).

Travel to a country of own choice. Enjoy its natural beauty and colours, the culture and diversity of the people, the laughter, the food, the music, the arts, the history. Make new friends. Take as many photographs as you can for you to look back on after many years. Buy at least one souvenir. Then share those splendid memories to family and friends and how your life-altering experience made you a better person. I'm thinking of India.

I believe that any demonstration of a large group (10,000+) of people working together and supporting one another. With out any financial involvement.

Loving someone until it hurts

That depends on the individual, what makes me better may not work for you. Finding that moment by accident and appreciating it is magical.

Real hunger

Surfing and sex.... least once.

Loneliness, impecuniousness, love, success - I think if people have and learn from these experiences they would understand what they need to be happy and content.