Studies typically find that unstructured judgements of the expected proportion who will get a question right typically correlate about 0.2-0.3 with the actual proportions (Bramley & Wilson, 2016; Attali et al, 2014). That means if you estimate the proportion as 0.5, the actual value will probably be somewhere in the range 0.2-0.8.
Left me hugely disappointed. Feels like, or at least looks like, teachers throw out a question hoping to hit a student with the correct answer. Even then, does being right mean, the students know why?