In this exploratory focus group study, we investigate which possible characteristics could be considered when selecting exercises for learners and how humans adapt exercise selection to learner personality and performance, so that an Intelligent Tutoring System (ITS) can tailor exercise difficulty to these characteristics. In six focus groups, we had discussed which characteristics of the learner and the exercise could be important for exercise selection. With participants playing the role of the system, we then showed validated stories conveying learner personality traits of Conscientiousness, Self-Esteem and Emotional Stability at high and low levels and an indication of their previous performance on a simple mathematics exercise. Participants were shown an example of the kind of exercises which would be given to learners of varying difficulty and asked to select the exercise which they thought the learner should do next. We observed that participants responded based on the personalities of the learners presented as well as their past performances, with learners high in each trait being given a slightly more difficult exercise than learners low in that trait and learners who performed better being given more difficult exercises than learners who had performed poorly.