Sure it is. There are some ways and various methods to bless ourselves and make different good luck/magic charms.
Anyone can take any necklace or jewellery and make use them as a charmed item, and a protection amulet. You can just simply charge it with positive energies and bless it by different methods you may find. There are simple methods of charming items and charging them with positive energy, by doing that you "bless" the item, and add your own energy so it's ,matched to your protection/blessing and your own energies.
It sounds like you are not the one who has charged it with positive energy, but in some cases you do that without even knowing to an item you feel special connection or love. Sometimes the good luck can come by your blessing and charging of positive energy (even though you do not know that you have charged it), and sometimes this is just a feeling of yours - that the necklace is the thing that brings all of the good luck... Basically, you do charge it with positive thinking and by the thought that it protects you and grants you good luck.
So you can say it's the necklace, and you can say it is the positive thinking and confidence. But you can also say that this happens because of both of the things :) Being positive is one of the things you makes you release positive energy and bless yourself.
I'd recommend you to look for methods of charging items with positive energy, so you'd be able to officially charge the necklace with your positive energies for protection.