Inventors are curious, love challenges, want to create something unique, make millions, see their product on stores shelves, but at what cost? I get contacted by Inventors all the time that are severely in debt because they spent thousands of dollars they couldn’t afford to lose. They jump head first into an industry they know nothing about and want to start at a higher level than really necessary to get some of the same answers.
Such as going to manufacturers to have a run of 5,000 units made in China before they even know if it will work properly. Then paying more to have the design modified to work the bugs out. This is being done before they even know if their idea is marketable. Instead you could make a crude prototype at home to see if you can find any bugs or design flaws. You can have CADs done to see your idea in 3D. You can go to local colleges to see if they would take on your product as a project for them to learn from and you get free work and a finished product to show proof of concept.
Paying for booths at trade shows to show a product that is incomplete hoping someone will see the same vision you have for it. When they could have just gone to the show to walk the floor and see what is there, their competition, make contacts, see how others present their products and what seems to work so when they do go and have a finished product to present they have a better understanding of how the shows work and how they might be able to draw more attention to their booth area. Because paying for a booth you have to man and have someone else free to wander the show can get expense.

Paying to have a full advertising campaign done, paying for trademarks, paying for local ads in the newspaper and radio promoting your product when you have no inventory and taking orders from people without knowing how you are going to fill those orders.
Starting KickStarters campaigns and severely under estimating what it will cost to fulfill the contributor rewards and not having a manufacture selected to handle your product.

These are just a few of the issues Inventors have come to me with that they learned a hard lesson that could have been handled better. Granted no one is perfect and mistakes will be made. You just want to lessen them as much as possible. One way to do that is looking at real life experiences of people here in the forums, the mistakes they have made, the lessons they have learned and are still learning, the information available to help you avoid pitfalls and make informed decisions.