孝 is a Logical Aggregate, formed from a upper part of character of 老 (literally means old, not young; old people, a venerable old man ) and a pictogram of 子 (literally means son; child). You can associate 老 with the parent, and 子 with the child, so the character of 孝looks just like a child carrying his parent on his back.
尽心奉养和服从父母 (support and be obedient to one's parents; filial)
In later Hàn dynasty lived a man called Jiāng Gé. His father died when he was young, and he lived alone with his mother. The times were troubled and chaotic, so, carrying his mother on his back, he fled. Again and again they encountered bandits who wanted to force him to join them. But Gé burst into tears and told them that he bore with him his mother whom he had to support. The bandits could not bring themselves to kill him, and at length he reached Xià Pèi in Jiāngsū province. Impoverished, naked, and barefoot, he hired himself out as a laborer to support his mother. His mother was able to have all she desired, and there was no end to what he gave her. A verse praises him thus:
He carries his mother out of danger;
When destitute brigands assault him many times;
He tells them his grief and is able to avoid them;
By his labors he supports his mother.