The are a set few reasons people don't finish construction once it is started:

1) They have excessive design changes that drive costs over budget. 2) A lack of organization means construction gets out of control. 3) They have theft, vandalism, injury, natural disasters etc. that aren't covered by insurance. 4) They pay people before they do the work, and the work doesn't get done, or doesn't pass inspection. 5) Their banking is sloppy so they pay some bills twice and some not at all. 6) Lack of results equals a stop in funding.

Proper planning easily prevents all of these reasons. How does planning help you to avoid these pitfalls? Why don't we look at each problem individually

Excessive design changes drive costs over budget:

If you start building before you have a clear idea of what you want, you are going to run into some major problems. You might change your mind about what you like, or how you want things set up. The problem with that is every change is going to cost you significant amounts of money. If you plan every detail and aspect of your future home, generally you will make far fewer changes to it once construction has begun, and the changes you do make don't cost nearly as much because they tend to be minor. They usually aren't the kind of changes that necessitate ripping out a wall, and reframing a whole floor.

A lack of organization means construction gets out of control: part of proper planning is organization. Thus, this won't even become an issue if you take the time to plan things out well. If you don't, you will have subs not showing up, or subs showing up for work and the building not being ready for them. For example, you might have a drywall sub showing up before the electrician shows up. This lack of organization equals wasted time, wasted money, and frustrated subs.

Theft, vandalism, etc. that isn't covered by insurance:

Proper planning is going to cut theft and vandalism down drastically just by only have materials on site for a few days before they are used, and having things done and secured quickly.

If you plan well you plan for the unlikely, and have insurance to cover it you will not have to quit building because of a natural disaster. Many builders think insurance is a waste of money, because you don't usually need it; but tell that to the tenth person that did need it. Proper planning covers all your bases, even the unlikely ones.

Contractors are paid before the work is done, or at least before a full inspection of the work is done:

This is a common problem. Often a new person to the construction scene will extend too much trust and pay subs upfront. But then they wonder why they are so far over budget when their subs never show and they have to pay another person to do a job they already paid for. Part of proper planning means having contracts for work, knowing when to pay what, and knowing how to have the work inspected to make sure it is good before you shell out the money for it.

Sloppy banking:

this problem will cost you so much money. If you create a system of organization for paying your bills, you won't need to worry about whether or not you paid a bill, and you won't pay the same bills twice. Instead, you will stay on top of things, and know when and what you paid for.

Lack of results equals stop in financing: your partner, spouse, lender, or whoever you have funding your project is not going to want to keep funding your project if they don't see their money being put to good use. If you can't show that the money will be used well, and that the project will stay close to budget and schedule, you are going to have a hard time convincing someone to loan you money. So, planning is essential, it means you have an outline to go by even if you end up varying a little. It means you have something to show your potential lender to instill in them a confidence of your ability to build a home.