But you can't always pick your providers. Example: You go to emergency room that is in-network. A month later you get the bill for the doctors that treated you - who aren't in-network.

"A new study that looked at more than 2 million emergency department visits found that more than 1 in 5 patients who went to ERs within their health-insurance networks ended up being treated by an "out-of-network" doctor — and thus exposed to additional charges not covered by their insurance plan." https://www.cnbc.com/2016/11/16/many-get-hit-with-surprise-o...