If their key players is not available, that could change the game even if the previous stats speaks for them. A book cannot give you these updates. You have to do it on your own.
Sometimes like to read news information on the internet for updates about the team while books can't help anything it's just basic gambling that is explained while it's different in sports betting, not only relying on luck but other factors affect it.
There are lots of information to read online regarding on everything what people need to learn with the sports they interest to bet and if they just read the official site,sports blogs and video reviews made by people with this provably that they might familiarized and have the latest news which provably could help them a lot towards their betting decisions.
Relying on luck won't bring good results and they might just waste their money for betting random things. So for people to have great idea better for these people to find good information about the team and know their situation since this give us more bigger chance to win.