It’s important to remember not to lead students to an answer or in any way reveal what they should learn. Big questions should lead to more questions, and don’t have a single right answer.
A SOLE can be fragile because a lot depends on the initial big question. If this question is not big enough or if students do not find it interesting or relevant in any way, they will use google to find the answer within the first 5 minutes and then disengage! This is perhaps the greatest challenge to address. How the question is introduced and the nature of the question is therefore critical. Some of the best big questions can often come from the students themselves.