Do not punish the report of a problem more visibly than the problem itself.

People learn quickly from what happens to the messenger. If reporting a fault brings interrogation, blame, or a long uncomfortable meeting, the sensible move for everyone watching is to say nothing next time and hope. The problems do not stop, they only stop being visible, and they arrive later at a worse size. What you meet with calm is what you get told about early.

Watch your own first reaction when someone brings bad news. Thank them before you ask a single question, and make the thanks as public as the problem was. If something needs correcting, do that separately from the moment of reporting.