If you are an expert and would like to transfer your expertise into a e-book than opportunity lays for you to earn money as e-books can be sold at Amazon, Barnes & Noble, Kobo, etc. One gets a hefty amount as above sites charge 30% commission which still leaves a lot for you on the table as marketing is being done by these websites.
So, if you are an expert than use your wisdom to earn money from the internet as only initial effort of writing is required and thereafter you can just relax and can benefit with the amount being generated by the purchases.
You can check out stock market books for beginners here.
