When we read books, we often see a few errors or gaps in proofs. Some typos are obvious and can be corrected easily. Sometimes there are more significant errors which forces us to "do an exercise" to fill in the gap caused by the error.
In the second case, since it is an "exercise", it's possible that we end up being unable to fill in the gap. If this is the case, then to ask a question here is an option. However, there are things which cannot be easily asked here - for example, if the gap appears in an expression, and the expression involves some notation which takes a few pages to define, and the notation is not "standard" (for example, some constructions doesn't have a name), then it becomes extremely difficult to ask for help.
What are some strategies to overcome this difficulty? How to prevent getting "stuck" on an error for a long time?