When we remember what something 'should' look like, we will often construct a memory to fit the mould. 

False memories can also happen to groups and could lead to mass delusions. People were shown a fake CCTV footage of a shop robbery and discussed what they’d seen. One of the participants introduced false ideas: the thief had a gun, right? Three in four people later recounted these fabricated ‘facts’ when questioned.

Scientists think that memories help us prepare for imagined future scenarios: If I do this, then that will be the result.

Sometimes a plausible guess, shown as a false memory, can be better than no idea at all.

• False memories can help us to find associations and connections. The most helpful memory might not be the most accurate.
• Incorrect memories of our past can help us to nurture relationships by facilitating empathy and intimacy with others. 
• Illusions can increase your confidence: if you remember that you solved a problem easily last time, you're more likely to solve it, even if you actually struggled the last time.