Lucky charm is an other name of addiction/obsession, it's like a belief.
for example: you always carry/keep A with you as it is very important in your life, you can't do anything without it and it always work for you, To keep A with you gives you confidence, like it's just a state of mind where you have state depending more on something/one then your own self.
The Sydney Morning Herald reports:
British scientists found that while carrying a charm had no impact on events based on chance, such as winning the lottery, those who believed in them felt more confident and optimistic. ... [A]lthough sceptical of any magical effects, these people felt more confident, secure and optimistic about the future, the survey found. ... Perhaps the most compelling statistic came at the end of the survey when participants were told they could give up the lucky coin -- 70 per cent said they would keep carrying it.
Source: <
http://atheism.about.com/b/2004/01/09/lucky-charms-dont-work-or-do-they.htm >
There is this other survey which has proved that lucky charms DO WORK because it gives confidence to do perform better <
http://www.dailymail.co.uk/sciencetech/article-1294985/Lucky-charms-DO-work-Study-proves-increase-chances-success.html >
It is (sort of) similar to a situation where people say they can't sleep without reading a book/watching something/listening to music..It's just a habit, nothing else.