Tactics are present in ALL chess games. It is just a matter of finding them.
To do that we analyze games played on Chess.com (and from other sources) to find games with blunders in them. Then we use a sophisticated algorithm to parse the results, making sure there is only one clear winning line.
Finally, we manually inspect each problem and select the ending position that makes the most sense. Then we upload them all and let people try them out! Those that have a very high fail rate are reviewed. We also also appreciate it when members report flawed problems!
Keywords: tactics problems source sources approve tactic method approving