How do I plan for difficult sites and things going wrong?

You can plan most missions well now. What still trips you is the hard site and the what-if that you did not see coming. That is the frontier of the skill, and it is exactly where planning gets real. The easy sites teach you the steps. The difficult ones teach you judgment, and judgment only comes from meeting them. The trick with contingencies is that you cannot plan for everything, so stop trying to. Instead, plan for the few failures that are most likely and most costly, and build in margin for the rest. A good plan is not one that predicts every problem. It is one that leaves you room to adapt when the unpredicted one shows up. Flexibility beats false completeness. For your next difficult site, before you finish planning, ask one question: what are the two things most likely to go wrong here, and what will I do if they do. Answer those two clearly and give yourself slack for the unknown. Over time, keep a short record of what actually went wrong on hard sites. That record will teach you faster than any checklist. Experience is just contingencies you have already met.