The first time I heard that was from my mentor (I’ll call her “Ann” here to protect the innocent). I was a new physical therapist, just about 2 years out of school, and I was having trouble with one of my patients with back pain. Ann asked me what was going on, and I gave her a very detailed description of my patient’s symptoms. Her response was a bit harsh, but well deserved: “You didn’t tell me anything that the patient couldn’t. You’re his physical therapist. What is the problem?”.
In an attempt to answer her question, I gave her a more detailed description of how my client’s pain changed with different activities. Ann cut me off after about 2 sentences (she never suffered fools well) and told me: “If you want to do this kind of work, the first thing you are going to have to learn is that pain is a liar”.