Ok, another idea... based on the "sunk cost" bias.

It's a simple investment game. User starts with a set amount of capital.

For the simplest version, you can invest in Stock A or Stock B - whose price fluctuates randomly (we assume we haven't enough money to affect the stock prices ourselves).

At any time, you can see how much your stock is worth now... and how much you have gained/lost so far... but also how much you could have gained if you switched strategy. Thus making it abundantly clear when it's better for you to switch to the other stock -> you eventually get better at noticing when your sunk-cost bias is actually hindering you.

probably needs some more work... eg more detail on how to calculate the various factors...