Have a Plan A. And then a Plan B. And then a Plan C. Go ahead and have as many plans as you need to have for you to get peace of mind.
Yes, focus relentlessly on Plan A, doing everything you must and you should – as if you have no other plan. But then if it fails, you move on to Plan B, because that’s why you have it in the first place.
You don’t have to moan about it. You don’t have to ruminate on it. You don’t have to beat yourself up on it. Do that if you must. Mourn and grieve the perfect Plan A that you had, if it helps you feel better. And then once you’re done (and you should be done as soon as you can), get on with it.
Plan B is now the Plan A.