According to https://stackoverflow.com/questions/8045235/infopath-2010-validate-i-agree-checkbox-before-submitting you can set a checkbox to "required" and it will validate that they have to check it before submitting the form.
But when I set this up, it does not require it to be checked. Is there something I'm missing, or is that first sentence in the answer just inaccurate?
Yes, I think the first sentence there is inaccurate. Later in the answer he says:
If required doesn't cut it, just add a validation to the checkbox, so it needs to be
true.
which logically makes sense: even though you are setting the checkbox to be "required" and have your validation as "cannot be blank", either state of the checkbox (checked or cleared) results in a valid value (true or false). A cleared checkbox is not equivalent to "does not have value."
So you need to add extra validation to only allow true as the only valid value.
The 'Cannot be blank' option works great if you set the 'Value when cleared' option to (blank) instead of FALSE.
