To say "relax" to someone undergoing stress in their body — either verbally or with your energy / hands / whatever — is a command that might not work well ... or, perhaps worse, it does work well and they "relax" via sedation / dissociation.
In my experience, this command can arise from a place of undigested emotional turmoil in the practitioner. (I know this well because, of course, that practitioner has been me! This is something I've seen through a great deal.)
It's frustrating. "Why are you holding onto this [story / muscular tension / idea about how this will go]?" I think. "Relax already; let it go ..."
But of course, when I say it that way, I am not relaxed, and certainly not fully integrated, in integrity with my thoughts.
And also of course, you would never get an abused dog to relax by telling it to relax.
You'd get it to relax by letting it know, deeply in its bones, that it's safe.
Relaxation, then, in the byproduct of much longer, slower, deeper and often less glamorous work.