You can't have two full time jobs (you ain't got a time turner, crazy fool) you have one job and you work hard at it. A job can be heaps of fun if you work alongside the right people and enjoy the work. It can be a pain in the arse if you don't have the right people by your side, because it's the only damn job you have and for the moment you have to stick by it. If your boss is a douchebag then it's going to be extra difficult to get along - they're the one in the driver's seat, after all (but that's a whole other metaphor, stay focused!). Even if your workmates are the best in the world, if your boss is a wankstain it's not going to be an easy ride. Changing jobs can be equally painful; if you move to a rival company then you're going to piss off the people you leave behind and workmates who became good friends can easily lose touch over time.
Don't get me wrong, if you enjoy your job and work alongside some really great people then you probably wake up in the morning (ie, log in) and think "DAMN I can't wait to get to work and start that freaking filing!". However, imagine if you work alongside some really great people and your working life is great, but then an old friend approaches you with an idea for a start up company - selling porcelain elephants.
It can't fail; its-a-freaking-GOLDMINE!
You'd have to leave those workmates behind to start your porcelain pachyderm factory.
(Still with me on the metaphor? About halfway now, how about taking a break: stretch and take a deep breath... ready to start again?)
In the new game the guild system is like going to a bar. Walk through the door and there could be any number of people milling about. It's likely you've come here with a few friends and that's great, but you know that there will be people in and out of this bar all night. You might choose to visit a few bars over the course of the evening, maybe jump from group to group and socialise with a number of different people. One night you might choose to spend the whole evening in a chill out bar, drinking ice cold vodka from frozen shot glasses. The next you might flit from sports bar to nightclub to strip club - you saucy devil. It doesn't matter if you decide to leave a bar and go elsewhere, you can come back later just as easily if the shisha bar across the street turns out to be a little crappier than you thought it would be.
If you're enjoying an ice cold beer with a group of friends from college (probably discussing the viability of starting up some sort of porcelain elephant production) and you're approached by the smoking hot barmaid from the pub just around the corner, you can excuse yourself from your current group - promising to return once you inevitably strike out - and attempt to woo the frisky young vixen with your talk of dynamic events and epic dungeon crawls whilst enjoying a cloudy ale and a packet of pork scratchings.
Besides, don't you spend most of your time at work wishing you were at a bar?
ps. the metaphor works equally well for class vs playground, but this was the more "mature" version.