The psychological differences of trading sim vs. real trading are truly monumental. Taking actions (trades) that result in real losses are much more likely to influence future decisions - not sticking to trading plan, trading opposite of the "system", wild trading, etc.
I know traders that consistently make profits in sim every week, but as soon as they go live and have a single -$1,000 day, they completely fall apart every time. Even a small loss causes them to abandon their trading plan, trade discipline, etc. because they psychologically cannot handle losses.
Put trading in a different context - say a basketball game. When you play a game of basketball, you take shots. If the shot goes in, you get points: 1 point for a free throw, 2 points for closer shots and 3 points for longer shots. If you miss, nothing bad happens per se except the other team may get the ball and they get to try a shot.
Now imagine if basketball games were scored different. If you made the shot, you get points. If you miss the shot, the same number of points are subtracted from you! If you take no shots in the game, your score would be 0. But if you miss more shots than you take, your score would be negative. Imagine how basketball games would be played if they took points away when players missed shots? I would suspect the game would be played radically different.
That is one reason trading is so difficult, "psychological acceptance" of true risk vs. reward is a very different concept that most people will only experience in trading.