diff --git a/lessons/effects.md b/lessons/effects.md
index c8620c05..65a7b64f 100644
--- a/lessons/effects.md
+++ b/lessons/effects.md
@@ -10,7 +10,7 @@ Since this Petfinder is a real service and we don't want to hammer their API, we
 
 `"dev:mock": "cross-env PET_MOCK=mock npm run dev",`.
 
-Now any time you run this `npm run dev:mock` instead of `npm run dev` you'll get mock data and not hit the API. This will work offline and if the API is down or taking too long.
+Now any time you run this `npm run dev:mock` instead of `npm run dev` you'll get mock data and not hit the API. This will work offline and if the API is down or taking too long (before running this, you many need to delete existing .cache and .dist folders to allow building in the mock mode).
 
 Now let's go install the client. Run `npm install @frontendmasters/pet`.