Third times a charm is an idiom which means that if one has had no success during the first two times, the third time may be one might be luckier.
1. Virender Sehwag had missed a triple century twice; perhaps the Delhi venue would work as a third time charm.
2. The site engineer was unsuccessful in the last two attempts in finding the source to put in a bore well; perhaps the third time would be a charm.
3. The athlete had missed the Olympic gold by a whisker on two occasions but third times a charm – he finally climbed the winner's podium at the Beijing Games.