diff --git a/documents/by-course/pstat-120a/course-notes/main.typ b/documents/by-course/pstat-120a/course-notes/main.typ
index 40961eb..f8b4f25 100644
--- a/documents/by-course/pstat-120a/course-notes/main.typ
+++ b/documents/by-course/pstat-120a/course-notes/main.typ
@@ -1322,6 +1322,9 @@ $
 
 for $k = 0,1,...,n$.
 
+The Poisson distribution is useful for finding the probabilities of rare events
+over a continuous interval of time.
+
 #example[
   The number of typing errors in the page of a textbook.