; sSomeone who has everything in life (fame, money, beauty) and the opposite, etc.) or someone who has almost nothing (someone who is poor, ugly, and so)etc.)?

For stylistic purposes, I have seen this in many contemporary novels, you could say:
A) Someone who has everything in life (fame, money, beauty, etc.) or
B) Someone who has almost nothing (someone who is poor, ugly, etc.)?

The truth is, that their happiness relyies on a lot of factors, like their perspective but, however hedonic adaptation ishouldn’t be forgotten as an essential factor here.

You see, to determinate if somethinga experience is pleasant or not, we always compare toit to our past experiences.

Let's imagine that both of them experience a positive situation (whether it's eating something delicious, or receiving a praise).

In that case, both of them will compare that situation to past situations and the one who lived worst things will be happier by the effects ofand experience gratitude.

Due to COVID-19 some of you maybe have experienced difficult times and I would like to share with you a few simple things toips that could help you havingto have a better life.

- kKeeping a gratitude diary

Choose a notebook or buy a gratitude diary in afrom Amazon and write 1 thing you're grateful for, for example how you feel after performing an habit you're used to doing.

- After you get up of your bedin the mornings, think or say "today is going to be a great day".

- Go to thea window and take 3 deep breathes whenbefore facing a difficult situation.

; sSomeone who has everything in life (fame, money, beauty) and, or the opposite, (someone who's poor, ugly, and so)whatnot.

I challenge you to rethink hard on your answer.

Since the author doesn't really know what the reader was thinking, it's a bit strange to ask them to rethink.

The truth is, their happiness rely on a lot of factors like their personal perspective but hedonic adaptation is an essential factor here.

"personal perspective" 个人视角
"hedonic adaptation" I didn't know what this meant and I'm a native speaker ^^; It might be worth explaining more.

You see, to determinate if something is pleasant or not, we compare it to past experiences.

Let's imagine that both of them people we listed above experience a positive situation (whether it's eating something delicious, receiving a praise, etc).

In that case, both of them will compare that situation to past situations, and the one who has lived through worst things will be happier by the effectswith a deeper sense of gratitude.

"by the effects of gratitude" the meaning is a little unclear

Due to COVID-19 some of you maybe have experienced difficult times and I would like to share with you simple things to help you havinge a better life.

- Go to the window and take 3 deep breathes when facing a difficult situation.

; someone who has everything in life (fame, money, beauty) andor the opposite (someone poor, ugly, and so on)

The truth is, theirone's happiness rely on a lot of factors like theirone's perspective, but hedonic adaptation is an essential factor here.

Although I understand you're using "their" to refer to the two hypothetical people, I still think "one" is more natural.

You see, to determinate if something is pleasant or not, we compare it to past experiences.

Let's imagine that both of them experience a positive situation (wheter it'such as eating something delicious, or receiving a praise).

In that case, both of them will compare that situation to past situations and the one who livexperienced worste things will be happier by the effects of gratitude.

Due to COVID-19 some of you maybe have experienced difficult times and I would like to share with you simple things to help you havinge a better life.

Choose a notebook or buy a gratitude diary ion amazon and write 1 thing you're grateful for after performing an habit you're used to doing.

- After you get upout of your bed, think or say "today is going to be a great day"

- Go to the window and take 3 deep breathes when facing a difficult situation.

; sSomeone who has everything in life (fame, money, beauty) andor someone who has the opposite (someone poor, ugly, and so) on).

I challenge you to rethinkconsider your answer carefully.

Your sentence is grammatically correct but this is more how'd we write or say it in the US.

The truth is, their happiness rely ies upon a lot of factors like their perspective but hedonic adaptationwhich is an essential factor here.

I'm not sure what you mean by, "hedonic adaptation," so this is my best guess at a correction.

You see, to determinate ife whether something is pleasant or not, we compare it to past experiences.

Let's imagine that both of them experience a positive situation (whether it's eating something delicious, receiving a praise), etc.

In thatis case, both of them will compare thate situation to past situationes and the persone who lived worst thingith less will be happier byecause of the effects of gratitude.

Due to COVID-19, some of you maybe have experienced difficult times andso I would like to share with you simple things to help you havinge a better life.

- kKeep a gratitude diary.

I write gratitude diaries both in English and in Japanese - yay!

Choose a notebook or buy a gratitude diary in aat Amazon and write 1one thing for which you're grateful for after perevery day. Repeating this will help forming an habit you're used to doingof keeping a gratitude journal.

- After you get up and out of your bed, think or say, "tToday is going to be a great day."

- Go to the window and take 3three deep breathes when facing a difficult situation.

We write out the number if it's 10 or less.