Do I Really Need a Packing List?
A goal without a plan is just a wish. Antoine de Saint Exupéry
It's not possible to overstate the importance of actually creating a personal packing list, and using it regularly. Such a list serves two principal purposes. First, it's a gentle reminder that if it's not on your list, it shouldn't be in your bag (because all the necessary items are on your list); this defends against last-minute attacks of "I might need this".
The worst possible time to be considering what to take on a trip is while you are packing for that trip!
Second, it helps ensure that nothing important will be forgotten. The go-light traveller in particular is only carrying items that are essential to the journey, so forgetting one of them can be especially inconvenient.
It's important to understand that you need a single packing list, not a new/different one for every trip. The purpose of a packing list is not to specify/record what you are taking with you on any particular journey, but rather to develop a model for your own travels, a constraint on your packing exuberance, a personal blueprint that you can refine over time (not change every time).
I've used the list on this site for more than a quarter century of travel around the world. I could probably reproduce it from memory. Still, I never fail to take the few seconds necessary to check it on every single trip. And, on more occasions than I like to admit, I've been reminded of items like a belt that I was forgetting to pack for the pair of trousers in my bag. It's no coincidence that aircraft pilots are required to complete a mandatory checklist — on each and every trip — before being allowed to fly the plane.
Don't pack list items that are unnecessary for a specific trip: parkas aren't needed in North Africa, nor are shorts in the Andes (for that matter, shorts are culturally inappropriate in many countries); malaria tablets & a mosquito net are unlikely to be helpful on a trip to San Francisco; dressy shoes might be dispensed with during an Amazon river trek; and you shouldn't need luggage locks when visiting your grandmother in Manchester (unless she has proclivities that might dictate otherwise). The list described in such detail on this site is intended to encompass items that are sometimes part of a one-bag traveller's needs, not always. It would be an unusual trip indeed that demanded everything on this list!
Add items if you must, to address your business needs, hobbies, personal requirements, etc., but resist the temptation to add non-essentials. If you're thinking "I might need this", you're likely mistaken; if it's "I can't survive without this", you may be right. But consider it carefully and dispassionately. Will the joys of listening to Radio America really warrant lugging that short-wave radio? Do you truly need that 200mm lens? Perhaps, though I have yet to hear of someone returning from an extended trip who.