The simple proxy's fallback function will take the data provided by the caller and forward that data as a delegate call to the implementation address, then propagate any return or error back to the caller. The fallback uses optimized assembly to achieve this efficiently. Since the proxy uses delegate call, the address of the proxy will have any state changes made in it, instead of in the address of the implementation. Therefore, if the implementation is changed, the new implementation will have access to the same storage. The only other function in the proxy allows a governance address to change the implementation address, which is called when the callback function executes.