Love what you do. I come here every day seeing people asking about how to make quick money and get into site areas such as finance, health etc...and Im pretty sure they dont like it, but just do it for the quick cash. Bad idea! Any topic can be a success, but the key factor is if you like what you do. If you enjoy your work, you will never feel stressed writing about it, you will find ways to market it and in essence, the quality of your work would most likely be pretty high, encouraging people to come back time and time again. Eventually you would be a success. Put fun in front of earning money because you will get money in the medium to long run.
If people on DP weren't so internally and monetarily focused, then maybe they would see how true this point actually is