Jack's parents caught him returning home late from a date and grounded him for a month. Robert was also caught arriving home late from a date, but his parents told him that as long as he gets home on time on subsequent dates, they will give him a higher allowance (though they will remove this increase if they catch him coming home late again). Neither set of parents catches every time their teenager gets home late. Why would we expect Robert to be home on time more often than Jack on future dates