Tweet, Tweet — Twiddle, Twiddle, here comes another plot with a hole in the middle.
If you fail to explain how A connects to B, or state something that doesn’t make sense (without explanation), then you have left a plot hole.
You want your readers to get swept away in your story and be completely immersed. A plot hole can destroy that experience. If the reader drops out of the ride, in order to examine something that doesn’t make sense, you’ve lost them.
You may be too close to the story to see the holes. As you read through it, those gaps may be appear bridged, since the story did come from your head. The answers to those questions are in your noggin, so it doesn’t seem off. Have someone else read through your book, to make sure you didn’t leave any plot holes.
Remember, the reader badly wants to be taken away by what you’re writing, so don’t destroy it for them.