A good coach distinguishes a lack of effort from a lack of understanding.

From outside, confusion and indifference look identical. The same hesitation, the same thing not done, the same blank expression while everyone waits. Reading one as the other is easy and costly, because a person told they are not trying, when in fact they did not understand, learns that asking is dangerous. After that the confusion goes underground.

Ask what they were attempting before you say anything about effort. Have them walk you through their thinking on the last attempt. If the answer reveals a gap, fill it, and keep any remark about willingness for a day when you actually have evidence.