All beings, no matter in whatever existence they may be, wish to escape from the sufferings of old age, sickness and death which are bound to be met as living beings. Nevertheless against their own wish, they are going through miserable conditions of life existence continuously through old, sick and eventually meeting with death. That is the reason why as a Buddha, he had taught his Dhamma knowing fully well that there was no Saviour other than him to save all living beings with his Great Compassion without regard to his discomforts and weariness. This also stands witness to the extent how he had to undergo miseries without having opportunity to gain happiness for, being deterred by his unparalleled Karuna.
Source: http://www.buddhanet.net