All hazards in workplaces are supposed to be identified, assessed for level of risk, and have the level of risk reduced to as low as practicable by the use of various controls. That's Health & Safety 101.
Yet we repeatedly see workers (also others, property, and the environment) being harmed because controls have failed.

This Workplace Safety Poster aims at reminding workers that HAZARD CONTROLS DO FAIL, making them and others open to injury or harm. This poster therefore asks workers to take hazard controls seriously and to ensure for themselves that they are appropriate and in good condition, and to take necessary action if not.

Of course this applies to all types of PPE as well as machine guarding. But often overlooked aspects of Controls are the Administrative ones including training, rules, procedures, and signs. 
 
This poster (and the associated graphic) can be used by those responsible for the health and safety of their workers to re-engage workers about their responsibility in monitoring hazard controls and reporting issues.  If you see an emergency exit blocked, do something about it; if wearing a mask is causing shortness of breath or dizziness or throat infections, report it; if you see a safety sign is obscurred, report it; if you notice new workers are not aware of procedures possibly due to training oversights, tell your supervisor. 

Whenever you notice a hazard control is failing or at risk of failing, act on it - for your safety, and the safety of others.