This is a ridiculous statement. Behavior needs to be repeated many times to develop fluency and then a habit. That's why it's important to support the safe work practices of our friends and teammates. For years I've wondered where the '21' came from. Then a local farmer reminded me it takes 21 days for an egg to hatch into a chicken.
Some behaviors are so complex or inconvenient they never become habitual.
Consider the chain of behaviors needed to lock out a power source, complete a behavioral audit, or follow a stretch and exercise routine. These important safety-related behaviors are never likely to become automatic. Their occurrence will probably always require some deliberate motivating influence, whether external or self-imposed. We can only motivate ourselves, not others. If this were true, we couldn't motivate others to choose the safe way of doing something when the at-risk alternative is more comfortable, efficient, convenient or perhaps habitual.