While Bryan Cranston and Aaron Paul were losing out over at the Emmys, their Breaking Bad characters were facing even deeper states of misery. Jesse, forced to cook meth for Todd's Nazi uncle and his pals, was trapped in a cage, his hands chained and his face bloodied. When he was caught trying to escape, his captors had him watch as they killed Andrea, and warned him that her son, Brock, could be next. Meanwhile, Walt was idling the days away in New Hampshire isolation, with no human interaction except for a monthly visit by Saul's vacuum cleaner guy. The man's updates on the White family's lives — Skyler was barely making ends meet, but she still had the kids, and was doing okay — both relieved and devastated Walt, who, even at this point, wanted nothing more than to provide for his wife and children.
Eventually, Walt's desperation grew so much that he made a dangerous trip to a bar in the nearby town and called his son, informing him of a money-filled package coming his way. Yet when Walt Jr. angrily rebuffed his offer, screaming at his father for killing Hank and otherwise ruining their lives, Walt realized that he was no longer needed by his family. Later, when he saw former friends and business partners Elliott and Gretchen Schwartz on TV, separating themselves from Walt and discrediting his contributions to the company, his anger began to boil. His family didn't need him, and they were probably better off without him. His former friends had needed him, once, but now, they were happily reaping success that they refused to admit he had helped create. Todd, Jack and Lydia didn't need him; they had Jesse to make the trademark blue meth. If he did "just die," as his son furiously ordered him to, no one would care. Walt ran away, and the world moved on without him, leaving him with no legacy, no need, no purpose at all.
That'd be a depressing realization for anyone to have, but for Walt — whose entire original motivation for cooking meth was to provide for those around him — it's what puts him over the edge. When he realizes that the legacy that he has worked so hard to build has vanished, it is his breaking point. Even after all that has occurred, his pride — his need to be needed — is larger than his sense of rationality and any trace of humanity he may have left. The smart choice would be to stay in hiding and allow his family to move on with their lives, but Walt is too arrogant to let that happen. He can't deal with the thought that his work has been for nil, and so he takes off from the bar, presumably to head back home and rebuild his legacy.
How this unfolds, we don't quite yet know; we've seen him take the ricin and a gun, but the victims —Todd? Jesse? Walt, himself? — are only mere guesses. What we do know, or at least what's been implied by this past episode, is that Walt's pride will ultimately be his downfall. He can't let his actions go unnoticed, and so he will do whatever it takes, even at the expense of his freedom and possibly his loved ones' lives, to make sure the world does not forget his name.