The topic is interesting and necessary - the formation of a financial cushion / reserves for the implementation of some plans.
And the model is not bad. Although I would add as one of the mechanisms of achievement - this is the rejection of bad habits and unnecessary purchases.
But what I do not agree with is to evaluate in a specific amount, for example, dollars. Different countries have completely different living conditions. And somewhere 3000 dollars a month is a small salary, in other countries it is an unattainable amount.
Therefore, the correct estimate is the percentage of income, and probably some coefficient, linked to the average acceptable level of income in the country. Then you get a realistically calculated level of monthly deductions to achieve some goal. And comparing $ 300 for the Congo and Switzerland, for example, is a useless topic.
I agree that the amount to be saved is subjective. It depends on the amount of the wage minus the amount need for needs. Most employees oftentimes have a shortage reason why they need to borrow money in order to patch what is needed then they will pay them with their salary and bonuses. Let alone this 1/3 of the monthly earnings, this is too much IMO.
If you are in twenties or early thirties and remain single, earn $3,000 after tax per month, you will probably save $1,000 if you, let's say, spend $500 to $800 on rental, a guest bedroom in a shared house/apartment, $500 on food, $50 on utilities, $150 on phone/internet bills, $400 on commuting costs or gas/maintainance if you have a used car, $200 on occasional entertainment or others. This $1,000 savings will allow you to invest or place a house down payment when time is ripe. Is this possible based on where you live ?
It's not possible where I live because $800 per month is considered a very good salary here, so saving $1k is out of question. But I think I can contemplate the possibility of saving 30% of your income. It's impossible in my opinion. It's too much. And those guys earning $3k per month, I'm sure they are living in places where everything, food, electricity, medical care and stuff, everything is more expensive there, so, they couldn't afford saving that much.
1/3 of our monthly income is not too much if we earn 4x of our basic needs plus bills. But for those who earned just enough for the bills and basic needs, the 1/3 salary savings is impossible.