Comment by adrian_b

That energy gain was only in the plasma, not in the entire system.

The extremely low efficiency of the lasers used there for converting electrical energy into light energy (perhaps of the order of 1%) has not been considered in the computation of that "energy gain".

Many other hidden energy sinks have also not been considered, like the energy required to produce deuterium and tritium, or the efficiencies of capturing the thermal energy released by the reaction and of converting it into electrical energy.

It is likely that the energy gain in the plasma must be at least in the range 100 to 1000, in order to achieve an overall energy gain greater than 1.