I tell clients that it's entirely natural to say "it's okay," as we are the dogs' caregivers, we love our pets. It's natural, but it's not okay.
Redirecting a fearful response is far healthier for the pet and will stick long-term. You can do this by using the dog's favourite treat (literally: something the dog loves to snack on). When your dog is exhibiting fear or anxiety and you find yourself starting to utter "it's okay," bite your tongue (often literally), and have the dog perform a simple command like "sit" or "stay" or "heel" and reward them immediately for having completed the task. This redirects the behaviour away from a fearful one and rewards the dog, rendering the entire experience a positive and beneficial one.

This is never okay!