A regional fintech company needs security controls that staff will actually use. Which security design principle emphasizes making protections easy to use and acceptable to people?

Defense in depth is a strategy of employing multiple layers of security controls to protect resources, not specifically about the usability of individual controls.

The economy of mechanism principle advocates for keeping security mechanisms as simple and small as possible, which aids in their analysis and verification, but doesn't directly address user acceptance.

The psychological acceptability of controls principle emphasizes that security mechanisms should be designed to be easy to use and acceptable to the individuals who operate them. If controls are difficult or cumbersome, users are more likely to find ways to circumvent them, thereby reducing overall security effectiveness.

The complete mediation principle states that all access attempts to resources must be checked by the security mechanism, ensuring no bypasses, but it doesn't focus on the human factor of usability.