I've been running my primary group through some Traveller lately. Last night after our game, which due to a few factors ended a little early. A few of us comment on how non-stressful it was playing Traveller. From the GM point of view, things have been really stress free when I compare it to other games that I have run. From the players' point of view there was not a lot of character maintenance. That got to thinking and asking the question why does it seem like it's so easy. I've come up with a few theories.
Maybe it's because there are less rules. Even with huge array of material available for Classic Traveller (CT), a lot of it's adventures and background. The combat rules are pretty easy and somewhat deadly, so there's not a lot there to get worried over. This means that combat happens pretty quickly and it generally doesn't turn into some huge mess. For both sides of the table, this is a great boon. You can actually have an adventure and not just run combat sessions.
While I am sure less rules is part of it, I'd submit that perhaps a reason it's less stressful is the system has no classes or levels. Yes, it does have former professions and what skills a character has is related to that but I don't think it's the same thing as a class and level. With classes and levels, a player advances on a somewhat set track. That power level on that track increases as the player gains levels. From a GM perspective, it means that adventures must compensate for this power. From a player's perspective, when they need to generate a new character, you either have suffer at low levels with higher level players or generate a higher level character. Both options are stressful, the lower level characters can't compete with the higher level ones and if you create a higher level character, you don't have as much organic growth as other characters may. In CT, without levels, most players are in the same playing field. Some may have a few more skills, but in general there are no closed options for players. Player can create new characters and bring them in at anytime without fear of them being too weak or powerful. Everyone is pretty equal in survivability or to put it another way, combat is deadly.
Of course, I'd be delinquent if I didn't suggest that it might be the lack of magic. Let's face it for both player and GM, magic is sort of a mixed bag. On the one hand it can be useful as an ally and on the other hand, it can be horrible enemy. From a GM point of view, it can be daunting to handle opposition that has magic. The players' party faces a party goblins with two goblin adepts (shamans). For the players having magic using characters is easy, they only have to keep track of their character. They have time to form strategies on how they will use their magic capabilities. For a GM, there is no suck luxury. I don't know how many times I've been stressed just trying to run an encounter, choosing what spells to cast for the opposition, and keep the game flowing. It's a mean feat. It can be done, but it is very taxing.
I'm sure I'm missing something. What are you thoughts? Why do you think some systems are less stress to run than others?