I've watched a lot of GDC talks in terms of how you should go about developing your game. There is an incredible amount of data that people have collected over the years that really drills down on people's behaviors and habits when playing video games. You can see a lot that has been implemented by comparing old games to new games. It used to be that you have to restart an entire level if you died, now you get checkpoints. Heck, even checkpoints are starting to be a thing of the past. You just respawn and keep going. All these little things inconveniences break the immersion of the gameplay and gets people to lose interest. This is why developers like Blizzard have added so many "training wheel" mechanics to their games. I've seen escort quests get "completed" status even if you failed, only because you had already put the time in to do the quest.