What you want to ask is why the man wants to give the woman a discount to buy a car after the engagement? The reasons are economic considerations and financial planning.

1. Economic consideration: The man considers the cost of purchasing the vehicle and the maintenance cost, and hopes to return this part of the cost to himself by way of discount. This is to share the economic burden or ensure one's economic independence.

2. Financial planning: The man has his own financial planning and hopes to invest the cost of buying a car in other aspects, such as real estate and education. Discounted car fare can provide more flexible use of funds.