I’ve often heard the sunk cost fallacy quoted as an argument for adoption of a different game system to the one you’ve already invested in. Thing is, when applied too broadly it becomes the ‘sunk cost fallacy fallacy’. Jonathan rightly added the caveat “even if it would be cheaper or better to abandon it for a new option”, but I think this point is worth expanding on because I tire of having people bandy the phrase ‘sunk cost fallacy’ about as if were some magic counter-argument.
Sunk cost applies to situations where you have made a bad investment, but are continuing to throw time and money after it because of what you’ve already spent, instead of cutting your losses. Classic example: Someone continuing to gorge themselves beyond the point where they are enjoying the experience because they have paid for an ‘all-you-can-eat’ meal and they want ‘value for money’.
But ‘sunk cost fallacy’ doesn’t apply to situations where you have sunk your costs into something the performance of which you are happy with and which promises to continue performing well into the future and deliver pleasing results.
Remember that costs sunk into collections of rulebooks for a system are the tip of the iceberg. The biggest investment in a long-running campaign is world-building and character-building. Even pre-published settings require a great deal of work to put flesh on their bones.
Now sunk cost would certainly apply if you were no longer enjoying the setting and characters, either because you had become disillusioned with the rules or had become bored with the setting and feel the itch to move on. But if there’s still plenty of life and vigour in what you’ve got, and you have plenty of unused material in the pipeline, then you need a pretty compelling reason to abandon your existing ‘investment vehicle’.
For many roleplayers, the mere fact that the alternative game system they are offered has the same name but with a sequentially higher version number isn’t a compelling reason to abandon their setting or carry out a gigantic migration exercise. It becomes even less compelling when what they regard as the critical success factors of their existing game system (for the purposes of their setting) aren’t even present in the alternative system under consideration.