What does luck have to do with all this? It is not like you are playing Bingo here or poker and hoping for good cards. It is all based on hard work, research, traffic and optimization.
I will say 99% hard word and 1% luck what i can see if only once or two time per day we are getting "surprise"
Its a combination of both because.. Some sites which you dont think will do well, seem to do well..and other sites whch you think would be popular dont do as well.. Promoting,link building etc. is hard work..but a good domain name can be luck..
The rewards come to those who want it the most. Those that want it the most are the ones that work the hardest. "Early to bed, Early to rise-Makes a man healthy, wealthy, and wise" this is true except when it comes to making money with Adsense. Sometimes you have to get up early and put in long hard hours just to get noticed. I wake up at 5 am everyday, spend time researching and learning more until around midnight each night. Marketing is a never ending class!