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Consider the complementary interaction

Sometimes creating the opposite interaction can have an even more powerful effect

Design is often one-way

When designing an interaction, there is almost always a complementary one to think of. Frequently, it’s more than one.

Sometimes we’re so focused on the task at hand that we fail to consider the rest of the picture.

Which leaves out important parts

As a result, the feature ends up being incomplete and significantly less effective than it can be.

This principle has three aspects:

  • Complementary data A simple example is categorization. A product has many categories. You might add a categories dropdown to products and call it finished. However, the opposite of a product having many categories is that a category has many products. Therefore, it’s a good idea to have a products dropdown in categories edit as well.

  • Complementary interaction An order can be paid. But a paid order can also be refunded. It can be delivered and returned.

  • Complementary point of view A message is sent, but it’s also received. Similarly, an order is placed and received.

Only after these three aspects are also taking into account can a feature be considered complete.

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