The phrase that shows how the ownership of the car changed the way the author regarded himself is: have thought myself a wise and fortunate man.
This phrase suggests that the author feels more confident and accomplished now that he owns a car. He sees himself as being wiser and more fortunate than those who do not own cars.
This is also supported by the rest of the paragraph, in which the author describes how owning a car has given him a sense of independence and freedom. He is now able to go wherever he wants, whenever he wants, without having to rely on others.
The fact that the author uses the words "wise" and "fortunate" to describe himself. These are words that are typically associated with adulthood and success. Additionally, the author mentions that he has been able to buy a car, which is a major financial accomplishment. This suggests that the author has matured and become more financially responsible.
Therefore, the answer is: have thought myself a wise and fortunate man.
The question probable may be:
In short, the thing got so badly on our nerves that finally, with full knowledge of the financial iniquity involved, I purchased one of those hopelessly plebeian affairs which travel under so many opprobrious pseudonyms-a Ford. From that day to this I have owned some sort of a car and have thought myself a wise and a fortunate man, and subconsciously I have felt myself rather more of a person because of this possession, for such is the frailty of human nature.