Because he does not succeed in controlling his time travels during an news years party held at his house. In his last moments with Claire he tells his wife that he is going to die soon and that he seen this since before in his time travels. Where his older self time travels in a forest during hunting season and is mistaken for an animal and gets shot by the hunters: "Why can't we do something!"[...]" stop it. Refuse to let it happen. Change it"[Claire ]" Oh Claire". Henry's voice is soft and I look at him, and his eyes shine with tears in the light"(Niffenegger 494).In his lasts moments he realizes that he must embrace fate let it have its way. All in All he had no power in changing his fate, thus there is a tragedy. Even though he tries to
