There are some good Sudoku apps which at each step offer hints and show to solve it systematically based on the current known information. I e.g. used the "Enjo

There are some good Sudoku apps which at each step offer hints and show to solve it systematically based on the current known information. I e.g. used the "Enjoy Sodoku" app for a while. With increasing difficulty level the steps become more and more less obvious, and I might not have come up with them on my own. I would say both trying to discover those methodologies on your own as well as using tools to learn about them counts as "training". So yes, I think one needs training to solve these puzzles at higher difficulty levels.