What is backwards compatibility?

Example: You upgrade your worldview from 'hard work always leads to success' to a more nuanced model that accounts for luck, privilege, and timing. But if your new schema can't explain why your friend who worked 80-hour weeks did become successful, you haven't upgraded — you've just swapped one incomplete model for another. Your evolved schema must handle every case the old one handled, plus the cases that broke it.

This concept is part of Schema Evolution in the How to Think curriculum, which builds the epistemic infrastructure for schema evolution.