The following contains spoilers for a section of the Last train quest line
I have been giving some thought to the time travel sequences in The Last Train set of quests and I realised that there are two very separate by equally fascinating paradoxs. The first the boot strap paradox of Said's Trinket. You first encounter Said's trinket when he explains that you need an item from the past in order to go back beyond a certain point. He says "I have no idea where I got this, but I have always had it so it must have had value". So we take Said's trinket and we travel back. finding ourselves in ancient Egypt where we meet a younger and very much alive Said who proceeds to pick our pocket and steal... the trinket. We, unaware that this has happened return to the present without the trinket. So the trinket never existed before Said lifted it and doesn't exist after we return. It quite literally exists between our being given it, our return to Egypt, Said lifting it and then holding on to it right up until he gives it to us. Where does the trinket come from?
The second is the paradox of the broken arc. We arrive in the under city of Al-Merayah to find the arc we needed was broken, and so we return to the past, and find a trap protecting the fully functioning arc, oh know we think to ourselves however shall we overcome this dilemma? Oh right we have this broken arc, if we take the functioning arc and replace it with the broken arc then we have solved the problem. we arrive back having thwarted the evil archetects plan to turn us into bee pancakes with the functioning arc which means that the broken arc we replaced it with is sitting on a pedestal awaiting us to arrive and claim with dismay OH NOES THE ARC IS BROKEN. From the very moment we arrived we were caught in a time loop that was unbreakable and unavoidable. The only reason we have to go back and replace the broken arc is because we went back and replaced the broken arc.