the principle that, to be perceived as different, two stimuli must differ by a constant minimum percentage (rather than a constant amount).

The principle you're referring to is known as Weber's Law. Here's a step-by-step explanation:

1. Weber's Law, named after the psychologist Ernst Weber, is a principle in the field of perception within psychology.

2. The law states that the change in a stimulus that will be just noticeable is a constant ratio of the original stimulus. This means that if you increase something by a certain percentage, that's the smallest amount of change a person can notice.

3. For example, if you have a pile of five papers and add one more, that's a 20% increase and you'll likely notice the difference. But if you have a pile of 100 papers and add one more, that's only a 1% increase and you probably won't notice the difference.

4. So, the principle is that the difference threshold is proportional to the original intensity of the stimulus, rather than a constant amount.

5. This law applies to all senses, including sight, hearing, taste, and touch.

6. It's important in many areas of psychology and also in marketing, where it's used to determine the smallest difference that can be made to a product that will still be noticed by consumers.