You have an almost unnatural luck about you. Not only can you use this trait every time luck or chance is involved, such as when gambling, you may also re-roll a single roll per session for as many times as you have value in this trait.
If you have +2 you may reroll up to two rolls per session. At +4 you may also roll an additional d10 on a single roll, once per session.
The additional die does not necessarily have to be used on the roll you choose to re-roll. They can be used independently.
This can also be used on top of Hero Points.