The following challenge is about the "memory loss" of your Sim. helping you getting to know your Sim and "their past" and build their life from scratch.
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Edit: Added a tip.
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Plot
Your sim wakes up in a small house with no memories, no friends and no job. Your goal is to help your Sim regain their memories and rebuild their life.

Rules

1. Create a Sim and pick their gender. Their personality and favorites have to be randomize. Keep their fashion style very basic, as you are going to find more about them during the challenge and change things as you progress.

2. Start with a small or a tiny house with basic necessities, such as a bed, a bathroom, and a kitchen. No TV or any other objects that increase fun.

3. As your Sim goes about their day-to-day life, they may start to remember things from their past. Pay attention to their thoughts and Wants, as they may provide clues about their past life.

4. Any interaction and any wish fulfilled provides information about your Sim's past. Who they might new in the past, their old job, their favorite object, Music, sense of fashion and so on.

5. Once your Sim starts to regain some memories, you can start to decorate their house with items that reflect their past life. For example, if your Sim remembers that they used to be a painter, you can hang paintings on the walls and buy them a Easel. Maybe some Sims reflect their past clothes and they want a makeover.

6. As your Sim continues to uncover more and more about their past, you can expand their house and fill their missing parts in life.

7. Finally, once your Sim has regained all their memories, you can decide what direction their life will take. Will they continue their old career, choose to stay with an old Sim they once knew or will they start fresh and pursue a new path? This is your choice!

Tip:
For a more interesting gaming experience, generate or make your own a short bio for your sim. A bio that says how they got to that place, who they knew, what they vaguely remember and so on. For example: "Liam's only connection seems to be a cryptic note mentioning a forgotten promise. Determined to unravel this enigma, he begin a journey to rediscover his identity. Along the way, Liam encounters a helpful neighbor named Sarah, who offers solace and encouragement. But who is Sarah?"
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Thanks for your interest, I'd be happy to see how people like it so far

Oh my gosh, I remember doing something very similar when I was playing years ago, first playing with NRAAS mods, and this post reminded me of it. I took a regular sim and I randomly added values to their skills, maxing out some, and having her realize a story that had happened. That fallen car in the Riverview river down by the criminal lord's house was hers, and she was targeted for some disputes, but got out with some amnesia. This sounds fun to revisit!

I'm glad it brought back good memories. I hope you enjoy the challenge =)

To be honest, this doesn't seem all that different from what the tutorial asks you to do. Instead of creating a completely new sim and pretending they have a history wouldn't the whole amnesia theme work better if you use an existing sim in whatever world you're playing in? Split them from wherever they are into the basic small house and just don't look at their traits and skills? Then they'd have an actual past to discover and even people they knew before that they could meet again.

Playing with premade sims can be interesting. But personally I find it more fun to play with a completely random sim.
If you want to take the challenge a little further, you can create a wheel that includes all the names of your Sims in the neighborhood and let it choose for you a number of sims your sim "knew" in the past.
For example, ex- partner, best friend, childhood friend.
The goal of the challenge is to create a story with random things that appear in the game or are decided in advance.
If I had known about a mod that pre-creates a family for newly created Sims, it would have made this challenge close to perfect.