This graph from 1976 summarizes all the other answers:
In 1976, it came down to a question of how bad we wanted it. Do we want it in 1990 (maximum effective effort), 1993 (accelerated), 1998 (aggressive), 2005 (moderate effort) or never.
We chose never.
Yeah its a media beat up.
The Wendelstein has worked far far better than other star in a jar’s… Yeah its currently worked for a QUARTER OF A SECOND.
actually their own aim , definition of success, is that it can work at 10 MW for half an hour.
So I figure they only have to make it last around 7000 times longer ! … its currently worked for around a 7000th of its target duration… is that working ???
Oh, come on. Be fair. No, it is not operating “far, far better than other star in a jar’s…”. It is only just started running and W7-X has only done one short campaign from Dec '15 to Mar '16, and that was just a lowish power trial to check systems (and to be able to tell the politicians the machine they had spent all that money on was operating!). Since then the device has been shutdown for the installation of the proper first wall and divertor. Once they are in and the machine is commissioned again - middle of next year - the power and length of pulses will start to shoot up (hopefully 
). Lots and lots of tokamak “stars in a jar” (stupid phrase!) have done way, way, better in plasma density and duration.
Except it is not just “an engineering problem”: modeling the behavior of plasma under these conditions is still not a complete science because of the inherent instabilities at these temperatures, and the problem of parasitic self-interaction within the plasma (Bremsstrahlung radiation) that prevents it from reaching and maintaining fusion temperatures in the core region (in this case, the core is the interior of the plasma toroid. And it isn’t just sufficient to get over-unity power output from fusion of the plasma alone; even after fusion is achieved, the energetic output needs to be converted into some form of energy that can do useful work. In a nuclear fission reactor, we run pipes of water, high temperature gas, or molten salt through the core to both keep the fuel elements from getting so hot they melt and to extract thermal energy (absorbed from neutron and gamma ray interactions) which can be converted into electrical power via a thermal exchange cycle and heat engine. Because the temperatures involved in nuclear fusion are so much greater than the mechanical properties of solid or liquid substance can withstand, this wouldn’t be feasible even if there is some way this could be done without interfering with the plasma. This means that thermal energy radiated from the plasma somehow has to be mediated (“thermalized”) to usable temperatures and/or energy has to be extracted from the neutron or charged particles that are emitted. There are several proposed means of doing this but one of the problems is that the high momentum neutrons will tend to damage any of the exposed materials, embrittling and for some materials making them radioactive. One of the possible mitigations would be to line the cavity with fertile materials which can absorb neutrons and be converted into fissionable materials, thus releasing energy in fission decay processes, but this is only a concept; no actual hybrid fission-fusion type reactor has been operated even at a proof-of-concept level.
As for the questions of the o.p., although we know fusion works since we can look up in daytime and see it in operation (or at night at the thousands of visible stars), and is fundamentally the source of nearly all of our energy, the degree of energy density required to achieve fusion in confined terrestrial conditions is charitably described as “extremely challenging”; in fact, it takes some of the most powerful machines in existence to produce fusion conditions for even a few hundreds of milliseconds and then requires extensive maintenance to function again, much less sustain fusion conditions for constant power generation. The W7-X offers some theoretical ability to better control and confine the plasma but still cannot maintain steady-state conditions for more than a few tens of milliseconds. The linked inquisitr.com article is just pop sci nonsense with numerous conceptual errors and appears to have been written by someone with no technical background transcribing sound bites from notes. It neglects to clearly indicate that the system hasn’t even been run at full operating power and has so far only going through system checks and low power operation.
Nuclear fusion, if viable, would be a boon to humanity because if it can be done cheaply and efficiently it would allow us to transition away from fossil fuels for large scale power production, could operate consistently without energy source fluctuations, and would potentially offer sufficient energy to synthesize liquid hydrocarbon fuels for transportation and mobile use in a net zero carbon emission fashion. But we aren’t anywhere close to even being able to plan for replacing conventional sources of power production (hydrocarbon, nuclear fission, wind, solar) with nuclear fusion. And if it turns out that it can only be done in gigantic, multi-billion dollar installations that require constant maintenance and materials replacement there remains the problem that it will be only within the capabilities of major nations, leaving the developing world still having to use hydrocarbon fuels. So it is far from a panacea at this point, even if it were theoretically viable.
Stranger