Packaging is an important element of the marketing mix. It signals whether the brand is a low price/value offering or a premium brand worth paying more for. It also helps regular buyers quickly identify the brand so they choose it without considering alternatives.
In this famous example, the packaging was changed so much that regular buyers could not find their brand on the supermarket shelf and therefore considered which other brand to buy instead.
A useful (albeit slightly verbose) explanation of this example can be heard in the audio clip.
Further discussion on this topic can be found in this LinkedIn post.