Hello, I do have tips, but I also have questions about your question.

Characters, how old are they? how old were when they started to live alone in the wilderness or in solitary confinement?

Time, what does long time means for you? months? years?

I ask those questions because we, humans, are social animals. We need others not only to get basics needs, but also to keep our personal identity. Since our birth we are in contact with other people from different backgrounds, socioeconomic status, personalities, age, cultures, among others. Sociology and psychology have theorized about this, since we grow and live in societies in two different ways, social and personal (not mutually exclusive), as a result we develop a social identity and an individual identity.

This is a lot of information, I’ll try to be as clear and organized as possible.

Sociology

Stages of Socialization

1. Family
2. School
3. Peers
4. Society

Here is a paper to help you understand this better: Socialization

Psychology

Theory of Psychosocial Development

1. Stage 1: Trust vs Mistrust
2. Stage 2: Autonomy vs Shame and Doubt
3. Stage 3: Initiative vs Guilt
4. Stage 4: Industry vs Inferiority
5. Stage 5: Identity vs Confusion
6. Stage 6: Intimacy vs Isolation
7. Stage 7: Generativity vs Stagnation
8. Stage 8: Integrity vs Despair

This theory is from Erik Erikson, here’s a link: Erikson’s Theory of Psychosocial Development

Cognitive Development

1. Sensorimotor Stage
2. Preoperational Stage
3. Concrete Operational Stage
4. Formal Operational Stage

This is from Jean Piaget: Piaget’s Stages

Theory of Moral Development

1. Level 1 Preconventional Morality: Stage 1 - Obedience and Punishment. Stage 2 - Individualism and Exchange
2. Level 2 Conventional Morality: Stage 3 - Interpersonal Relationships. Stage 4 - Maintaining Social Order
3. Level 3 Postconventional Morality: Stage 5 - Contract and Individual Rights. Stage 6 - Universal Principles

This theory is from Lawrence Kohlberg: Kohlberg’s Theory of Moral Development

Why do you need to know this? Because if your characters are alone in the wilderness or in solitary confinement since a young age and for a long time, all those stages will be affected.

Here are some examples

10 Modern Cases of Feral Children

“Blindfolded & bound”: Israel puts more Palestinians kids in solitary confinement  (remember context)

Living in the Wilderness

After you’ve got the age of your characters, you need a purpose, especially if they’re teenagers or adults. Sometimes it can be discomfort with society, sometimes because they want to live alone, sometimes for spiritual fulfillment, sometimes because circumstances made it possible. You have to consider their resources and what they know about nature, if they carry something with them or have to figure it out how to live with things nature provides. And the place where they want to live is important as well, are your characters prepared for the wheater? are they going to live in a rainforest, somewhere near a beach, near a river, a mountain, desert? Something else, can they live there? who owns the land they want to live in, the government, is it a national park, native land? What happens with their houses, family, taxes, etc?

10 Modern Day Hermits

7 People Who Gave Up on Civilization to Live in the Wild

Is it Legal to Live in the Wilderness (doesn’t give any answer to the question but there are a lot of experiences)

Going Alone in Wilderness for Self-Renewal

The Walden Effect: Tracing the Myth of the Man Alone in the Wilderness (this one brings the question of why there are more men than women willing to live in the wilderness, the answer is very vague, if you can bring up an answer or some hit in your story give it a try)

Realities of Going Primitive (careful with the terms primitive, native, “Indian”, and civilization)

Solitary Confinement

Unlike living alone in the wilderness, solitary confinement goes against the person’s will. This is related to imprisonment, kidnapping and war crimes, is also meant to inflict some kind of damage in the person’s mental and physical health.

What Solitary Confinement Does to the Brain

What Does Solitary Confinement Do to your Mind?

Taking the Solitary Confinement Debate Out of Isolation (this one is about prisoners with mental illness in solitary confinement)

Solitary Confinement Facts

The following links are about children and youth in solitary confinement

The Psychological Effects of Solitary Confinement

Growing Up Locked Down - Youth in Solitary Confinement in Jails and Prisons Across the United States

Should Children Be in Solitary Confinement?

Identity

As said before, humans are social animals, our identity is made, among other things, by our experiences, memories, and our surroundings. I’m not this, I am that, I like this, I dislike that. The way we see ourselves is part conditioned by our relationships with our environment. So, what happens when there’s no one around to valide us, to makes us believe that we are what we think we are or what we aren’t?

Brain

Solitary Confinement doesn’t involve just your interactions with other people, but also involves your brain and external stimulus. As long as there are things for your brain to keep it working it will work.

What Extreme Isolation Does to Your Mind

Sensory Deprivation Can Produce Hallucinations in Only 15 Minutes

How Extreme Isolation Warps the Mind

Context

Always remember context, especially for solitary confinement. Why there are people being imprisoned? And why solitary confinement is being used.

Final Considerations

The age of your character is one of the most important things when they were imprisoned or decided to live in the wilderness, or were left abandoned, or escaped, or got lost.

If they were imprisoned, what was the reason? why are they still in solitary confinement? Show us the process they’ve been through (you will need more research), are they still the same? if they are free now, how do they live? where do they live? how do they react to sensory stimulus? Is it a prison or another 

If they’ve been living in the wilderness, how do they live? why they left their homes? is someone looking for them? Do they still have some kind of contact with people?

There’s still the debate about nature/nurture. Are we a product of our genes and our environment or does one of them has more impact in our life? The way we are is because the way we were raised or because we have that written in our genes? When writing characters living in the wilderness for a long time and since their youngest youth you can explore this in your story.

I think I forgot Freud and his theory of development. But I think you got the general idea of the things you have to keep in mind.

Hope this can help you.

L.-