diff --git a/README.md b/README.md
index 96de3d2..2fce0c5 100644
--- a/README.md
+++ b/README.md
@@ -129,6 +129,9 @@ Profile key metrics for WordPress hooks (actions and filters).
 wp profile hook [<hook>] [--all] [--url=<url>] [--fields=<fields>] [--format=<format>]
 ~~~
 
+In order to profile callbacks on a specific hook, the action or filter
+will need to execute during the course of the request.
+
 **OPTIONS**
 
 	[<hook>]
diff --git a/inc/class-command.php b/inc/class-command.php
index e0e6be5..4b0e011 100644
--- a/inc/class-command.php
+++ b/inc/class-command.php
@@ -85,6 +85,9 @@ class Command {
 	/**
 	 * Profile key metrics for WordPress hooks (actions and filters).
 	 *
+	 * In order to profile callbacks on a specific hook, the action or filter
+	 * will need to execute during the course of the request.
+	 *
 	 * ## OPTIONS
 	 *
 	 * [<hook>]