A die-hard dedication to training, I'm coming to realize, must be accompanied by an equal dedication to rest and other factors that sane, non-runners take for granted.  A prime example: there was a time (ok...like most of my running career) when I considered cross-training days to be days "off."  You see the rationale I'm sure, since these days did not include a run they were a waste and counted for nothing.  To me, like to any logical human being, a 4000 yard swim takes no effort and actually constitutes rest.  Now that I am old and wise (a slight exaggeration, perhaps) I'm coming to realize the tremendous benefits of cross-training.  Time in the pool allows me to gain strength without pounding my feet against the ground a few thousand times.  Another benefit is endurance, especially if swimming is your preferred cross-training method.  When I swim regularly my breathing become increasingly efficient.  Translate this into running - a setting where you can breathe whenever you want without risk of asphyxiating yourself on highly chlorinated water - and you feel like you can go forever.  Lastly, as I discussed in a previous post running is such a mental game.  Along with the anxieties, competitiveness, and doubt that swirl in many runners' brains there can also be a degree of boredom.  I'm sure I'm not the only distance runner who occasionally dreads running 8 or 10 or 12 miles alone with nothing but my thoughts.  I definitely cannot bring myself to swim more than once or twice a week, but staring at the bottom of a pool does make the runs feel special and exciting, not to mention when I hit the trails the day after a swim I feel like a gazelle in it's natural habitat, as opposed to a gazelle that has been dropped into a pool.  The moral of the story is that cross-training may not be running, but that's the point.  I'm teaching myself to respect cross-training as another valuable training tool and as hard work and not a quasi-day-off or a sign that I'm not sufficiently dedicated to the sport.  It's hard work, it expects my body to do something totally different which is both a blessing and a curse.