Even that analysis can lead you astray. If you only need a small car for essential life function L but opt to buy a bigger car because every few weeks you want

Even that analysis can lead you astray. If you only need a small car for essential life function L but opt to buy a bigger car because every few weeks you want to take the entire family out to dinner then it's not reasonable assign the entire fixed cost to L. The calculation becomes more complicated: a smaller car is likely cheaper to operate for L, and the cost savings over using a bigger car for L may be enough to pay for a taxi or ride-hail for the occasional times you need a bigger car for dinner, or to pay for a rental car for a vacation trip, or to pay for delivery if you need a large volume purchase.