Here are some examples:
* "The task seemed insurmountable, but they persevered and eventually succeeded." This means the task was incredibly difficult, but they were able to overcome it.
* "The financial losses were insurmountable, leading to the company's bankruptcy." This means the losses were so large that the company couldn't recover from them.
* "The mountain climber faced an insurmountable challenge in the treacherous conditions." This means the conditions were so dangerous that the climber could not safely continue their ascent.
Essentially, "insurmountable" emphasizes a level of difficulty that is seemingly impossible to conquer.