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Scientists have discovered a scientific reason why it is difficult to find a needle in a pile and often leads to failure.

If you are a security officer at the airport, and you have to check out 600 bags, 15 of them contain a few strange weapons, often you can't find all 15 bags.

Corresponding to the number of objects, searchers will make more mistakes if the object they find is less common. According to lead researcher Jeremy Wolfe: 'If you don't have to find it often, you usually won't find it.'

Pile of straw is the perfect refuge of a needle.

Researchers from Harvard found out why this happened. They used 12-13 groups of volunteers to study the bags that had been confirmed by the machine.

The usual senses may tell you, because what you rarely find is in the box / bag where there are lots of boxes / bags, your brain will immediately get used to repeating that. 'It is not there'. And so you start forgetting what you're looking for.

The new research shows that the answer is: 'It is already' coming more slowly with only very few things.

This is an adaptive activity that in the time of human ancestors, if you find food you will be more likely to be in food-rich places and less likely to stray into areas with very little food.

The conclusions that have been found may be useful in training airport security personnel or radiologists to discover more cancers on film copies. According to the research team, if these professionals spent two minutes trying to find conventional weapons and tumors, they might do a good job of finding more rare things in the next 30 minutes.