Buddha Shakyamuni lived the life of a worldly prince, then went to the forest and practiced rigorous asceticism, before his enlightenment. He thus spoke authoritatively about extreme views and behaviors that do not and cannot secure happiness.
All the Buddhas and Great Bodhisattvas have had ordinary human experiences. Whether those experiences have been voluntarily assumed or driven by the winds of karma is a matter of contention, but that they have had them is universally accepted.
That is how they understand ordinary beings and are capable of assisting us through skillful means. They have experienced wrong views and afflicted emotions, and have attempted various remedies to remove them.
They can empathize with our mistakes, and we can learn from theirs. They have realized the Buddha essence, and we can also realize ours by following their example.