Preparation is never wasted
Have you ever prepared to get ready for an event only to get there and discover that you had mistakenly taken the start time to be 1 hour earlier than it should have been? As annoying as that may be, you do find that being earlier or on time has many more advantages than being late.
In light of this, can one ever be over prepared or can preparation ever be a wasted effort? If we are to find out from a host of people what their experiences have been with regards to preparation, we would find more that would have suffered for not preparing, and almost none that would have been disadvantaged by overpreparing.
It is good practice to always have more than you need for any tasks that you need to do. If it takes an hour to do it, budget an hour and a half. If you have to spend a hundred pounds to build it, budget a hundred and fifty. If you need a couple of changes of clothes for the journey, take one more set. Consider your situation well and what needs to be done then always prepare for just that little extra. Preparation will never be a wasted effort.