Faulty presumptions, around which trading plans are so often built, can often be the undoing of aspiring traders.
Surprise market events are these troublesome things that happen when people are busy making other trading plans.
Imagine an umbrella that typically works on sunny days, and often fails in stormy weather!
(Can you see how this analogy might relate to your recent experience?)
Ideally, any long term trading plan, needs to incorporate safeguards against all likely market behaviours.
Price gaps are very much a feature of many markets and, as such, should ideally be given due consideration, when incorporating risk management practices into one's trading plan.