Mark the minority of inputs in a form as required or optional

In a single form, mark only the required fields or only the optional fields, depending on whichever is less frequent in the entire form.

If most of the input fields are optional, only the required fields should be given an asterisk icon or have labels appended with "(required)." If most of the input fields are required, only the optional fields should be appended with "(optional)." An asterisk icon should never be used to note that a field is optional.