23 of 365 – Constraint design principle by John LeMasney via lemasney.com
Constraint is built into systems to allow limits to negative actions a user might otherwise take in that system. In mechanical systems where too much power, volume, or other resources could be over-applied, constraints prevent the user from doing so. We also can be psychologically or physically constrained from entering dangerous areas by a do not enter sign, or areas where our presence might cause alarm or discomfort, such as a bathroom intended for the opposite sex.
In this illustration, I made a constrained variable slider control going from low to high, which does not allow for setting too low or too high.
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