please someone explain I am totally lost...
You have to put the effort in. There's a minimum amount of effort you have to put in, to complete the project. To get a fort built, you
have to put in a minimum of 100 days of personal effort (= downtime days) supervising the construction. Okay, it's not very heroic and you'd rather be doing something more exciting but how badly do you want this fort?
If you start a build and then take your eye off the ball, things will start to go wrong. In a single day, so much will go wrong that it will take you two days extra work just to haul the project back on track. Then you still have to finish the project. The more you let things slide, the worse it gets.
Let's take an example. Suppose today is the day the masons are going to put the windows into your castle. The carpenters made all the windows yesterday while the masons were preparing the apertures, and now the masons can put them in, today, while the carpenters are working on the roof. Now, you decide to take the day off carousing and leave them to it. What's going to happen? Murphy's Law applies. The masons will put in the windows upside down (so the rain runs in instead of running off) then cement them in. You come back tomorrow and it's all gone pear-shaped. You tell them to rip out the windows (which takes a day) then the carpenters have to make a new set of windows (which takes another day, and you'd better be there to see they do it right) while the masons have nothing to do, then the day after that, the masons can fit the new windows (and you'd better be there to see they don't put them in back to front this time) while the carpenters go back to making pieces of roof, which they have to start all over again because it's been raining. Net result? Two extra days of your time spent getting the mistakes ironed out, just so you can get back to where you would have been several days ago if you hadn't been carousing.
If you think the windows example is absurd, there's a building not a million miles from where I live where the self-cleaning windows, which have spray nozzles on the outside to wash the glass, were put in back to front and no-one noticed until the people inside the new offices and their brand new furniture were liberally sprayed with water the first time the cleaners turned on the window washers. The owners baulked at the cost of refitting all the windows, so they decided to abandon the self-washing system and use mobile gantries and men with sponges. But the gantries were too heavy for the walkway around the building so the walkway had to be dug up to lay stronger foundations. Which meant digging up all the service ducts that were laid under the walkway. And so it went on.
You can't just order a fort and come back when it's finished. You have to be there all the time making sure it's done right, otherwise it won't be.