Let’s imagine you are building a small rectangular house. It’s a simple structure, just four exterior walls, and a couple of interior walls. As you are about to finish, you realize you want one of the interior walls moved 2 feet to make one of the rooms larger. You will have to knock the wall down, fix whatever damage was done to the exterior walls and floor, and then make sure the new location of the wall can handle the stress etc.
The alternative is to create very detailed architectural drawings and plan things out properly from the start. By doing this, when you realize you want a one of the rooms to be larger, you simply erase the original line, make sure everything will work and then redo the drawing with the larger room.
The second option will require more time in the planning phase but will ultimately take less time (and less money) then the unplanned option.
Spend the time planning and long term, things will be cheaper, quicker and better.
The one caution here is to not get caught in “paralysis by analysis”. Don’t let your planning stop you from ever starting. Things will never be perfect so do proper planning but also be willing to move on.
Have a great day!