The doctor is not infallible. He or she is likely extremely busy, and under many pressures, e.g.:

- patients who adamantly insist on X treatment, make a fit and threaten a bad review, even though they don't need it

- fear of malpractice suits (e.g. 99.9% chance treatment is unnecessary and a waste of money, but in the 0.1% case I might get sued to oblivion if I didn't prescribe it)

- intense lobbying from pharma companies who spend boatloads of money trying to convince them to prescribe their products

In general, they don't directly pay the costs of using limited healthcare resources, but they can pay serious costs for failing to use them, so their incentives are skewed.

Our current system is far from ideal. But a system where a single person gets to make all the decisions, while foisting all the financial burden on someone else, would collapse within a week. Someone has to be the bad guy to sometimes say "we can't afford this, sorry".