For example, being reckless in demos, as you know you are not going to lose money in demo accounts, you might develop the trait of being too reckless. It can't be done in live trading because one wrong trade might burn all your funds. Treat the demo account like you are trading live.
This is the reason why newbies should not start with demo trading accounts instead they can start with small capital like $50 or 100 or whatever the amount feels nothing to lose that may not bring complete emotions like intense trading decisions but it's a lot better cause it's real money so when you lose you feel that you need to do something about it and that's how we can master the emotion management while doing trading.