It's a machine that changes reality, your memories you be replaced (for as long as you are connected) and you can't differentiate what is happening to you with reality.
Here, Law changed Jesse' memories to make him think he lost everything, so that he's depend entirely on Law, but Jesse (being so smart), always knew something was wrong and rejected Law. And this happened again and again, each time Law started the experiment again in the hope that it'd end differently.
The last time (the one we saw since the beginning of the manhwa), Jesse finally chose Law and it succeeded.
He didnt make Jesse "think" that he lost everything, he actually lost everything. But strictly speaking only inside Moritat.
Thanks I get a little idea now
I finished reading this.. then again re read it.. but I still can't understand what moritat is!
I mean how does the machine work?