I hate uncertainty. I'm also a big sucker for to-do lists and love planning things meticulously. Especially when going to the gym, I hate walking in there without a real plan of what I'm doing. I think that's why I am such a big fan of Kayla's BBG guide, or any type of workout guide really.
Taking on a ‘mission’ like "I want to get fit" without a defined goal or a plan is the same as walking out of your front door and not knowing where you are heading. If you have no plan and no goal destination, how can you push yourself to achieve that goal? Goals allow us to succeed and success keeps us motivated.
I've been working out regularly aka approximately 6x a week for the last 3 years now and have always followed some sort of guide or self-made plan with semi-realistic goals (alright fine, I still can't do the splits, I still can't do 5 pull ups in a row and I still can't walk in a handstand, so the whole "achievable" part of my goal setting hasn't really worked out that well for me yet...).