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+---
+visibility: public-edit
+---
+
+# "it works on my machine"
+
+*(common gotcha)*
+
+## what happened
+
+your project runs perfectly on your laptop. you demo it on someone else's machine (or the judges' machine) and it crashes immediately. different OS, different Python version, missing dependency, hardcoded file path.
+
+## why it's a gotcha
+
+local development hides environmental dependencies. you installed that library 6 months ago and forgot. your code uses a Mac-specific path. your Python version has a feature that older versions don't. you don't notice any of this until you're on stage.
+
+## the fix
+
+test on a clean environment before demo day. docker is ideal but even just testing on a friend's laptop helps. document your setup steps. if your demo depends on your specific machine, you're one coffee spill away from disaster.
+
+## see also
+
+- [[test-demo-before-presenting]] — test on the actual demo machine
+- [[restart-server-before-demo]] — stale environments are a subset of this
+- [[no-backup-plan-for-failed-demo]] — when it doesn't work on the demo machine
+- [[not-using-version-control]] — track dependencies properly
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