https://en.wikipedia.org/wiki/Survivorship_bias

Basically the story goes that planes would fly to the battle field and come back with bullet holes. Experts started charting where the bullet holes (as you can see in the top image) and decided to reinforce the armor in those areas since they were “the most commonly struck by bullets”. Makes sense!!! Exceptttttt… those were the planes that survived, meaning that the bullet we see in the image do not explain why planes fall in battle. Places that have no bullet holes in the image are the areas that, when struck by a bullet, would cause the plane to fall. When they started reinforcing the areas that have no bullets in the image, “plane survival” increased significantly.

I hope my explanation is understandable!

The issue is called "survivorship bias". The image you are looking at are from WW2 bomber planes that got damaged during missions but still made it home in one piece. The red dots are damage from enemy fire. The engineering task was to identify structural weak points and make the planes more resistant to enemy fire.

However the data on plane damage is grossly incomplete, because only those planes that survived are included in the data set. Those planes that took critical damage exploded and are not available for examination.

With that in mind, look at the diagram again. Those areas that do not have any reported damage are the actual structural weak points of the planes.

https://en.wikipedia.org/wiki/Survivorship_bias