In an Insurance Markets, how can Adverse Selection affect it?

-If a Firm engages with Medical Insurance, it will Calculate the Insurance Premiums (Cost of Obtaining the Policy_ based on People it will think will Buy it -The Premiums may be too High for the People that would want to Pay it - like Healthy People (who are Ideal) -But it would be good for Poor Health People, who will be a Drain on the Firm's Liabilities -The Insurance Firm will thus be making a more Unprofitable and Riskier Balance Sheet, which was Unexpected