stepping-stone

n. 1. A stone to raise the feet above the surface of water or mud in walking. [ 1913 Webster ]

2. Fig.: A means of progress or advancement. [ 1913 Webster ]

These obstacles his genius had turned into stepping-stones. Macaulay. [ 1913 Webster ]

That men may rise on stepping-stones
Of their dead selves to higher things. Tennyson. [ 1913 Webster ]