There are two types of failure: ignorance (misunderstanding of how the world works) and ineptitude (failing to apply our knowledge correctly). Advancements in science have tilted failures towards ineptitude.
For example, heart attack patients who would benefit from cardiac balloon therapy should have it administered within 90 minutes of arrival. In 2006, an average hospital had less than 50% chance of achieving testing, informing patient and obtaining consent, confirming allergies, readying a cath team and starting the therapy within 90 min.
It’s not about the capabilities of the professionals - they spend lots of time learning their field. However, the volume and complexity of what we know exceeds our ability to apply it correctly, safely and reliably. A checklist helps us overcome these inevitable human inadequacies.