In Gary Paulsen's Hatchet, Brian's first bow nearly spells disaster for him because when he tries to test it, the bow wood explodes in his hands, sending deadly splinters and wood chips into his face. Two sharp pieces actually lodge in Brian's forehead, just above his eyes; had they landed slightly lower, they would have blinded him, inflicting a devastating injury that would have seriously compromised his ability to survive (Chapter 13).

Brian had actually made a previous attempt at fashioning a bow, but before he had gotten very far along, that attempt too had almost ended in disaster, because it triggered a series of events that very nearly caused him to give up hope. In that incident, Brian had carefully chosen a branch with "an almost vicious snap" to it to make a bow. The wood was hard, and he had been concentrating so intently on carving it correctly that he had not at first heard the "persistent whine" of a passing plane. When Brian had finally become aware that rescue might potentially be near, he had thrown down his bow and run to light his signal fire as fast as he could, but just when he had finally gotten the flame to feed, the plane had turned and disappeared. Brian had been so devastated by this event that he had given up hope of ever being saved, and had gone so far as to try to kill himself.

Brian was eventually successful in making a serviceable bow, but both of his early attempts were unsuccessful and dangerous. The author says that Brian's first bow "was a disaster that almost blinded him," and this turns out to be true both literally, when it almost causes him to lose his physical sight, and metaphorically, when it nearly causes him to lose sight of his determination and resolve (Chapters 12-13).

In the book Hatchet by Gary Paulsen, how does Brian's first bow nearly spell disaster for him?

More than that, Brian's first attempt at making a bow for his arrows comes close to blinding him. He has made the bow "too stiff"; it snaps, sends pieces of wood into his face, an inch or so above his eyes (p 124-125). Brian is indeed able to see the incident as one of many in which he has learned valuable lessons, though. The first bow "looked beautiful"--but the looks were deceiving, almost costing Brian his sight. In that setting, that would be probably have been fatal.

In the book Hatchet by Gary Paulsen, how does Brian's first bow nearly spell disaster for him?

Like so much of what Brian endures, there seems to be an ongoing dialectic where he experiences something bad, following by something good, succeeded by something bad.  The bow incident is no exception to this.  His experience with the first bow spells near disaster for him, as it almost ends up wounding him.  I would pay attention to Paulsen's description of this event in the middle of the book.  Brian is able to understand how the bow was calibrated incorrectly and nearly hit him.  He grasps this, makes the modification, and then is able to produce a bow that is able to hit the fool birds and generate both a new source of food production as well as protection device.