If a life is to be complete we must not stop with this dimension [length]. There are some people who never get beyond this first dimension of life. I’m sure you have seen such people. These people are only concerned about themselves. They seek to achieve their ambitions at any cost. They brilliantly develop their inner powers, but they live as if nobody else lives in the world but themselves. Other persons become mere steps by which they climb to their personal ambitions. There is nothing more tragic than to see a person bogged down in the length of life devoid of breadth.

Martin Luther King, Jr. (1929–1968) American clergyman, civil rights leader, social activist, preacher

Sermon (1954-01-24), “The Dimensions of a Complete Life,” Dexter Avenue Baptist Church, Montgomery, Alabama
    (Source)

The italicized text at the end is from a different draft.

This was one of King's favorite sermons, possibly originating in 1952, and he reworked and delivered it (or reprinted it) throughout his life. Other versions:

But don't stop here; it is dangerous to stop here. There are some people who never get beyond this first dimension. They are brilliant people; often they do an excellent job in developing their inner powers; but they live as if nobody else lived in the world but themselves. There is nothing more tragic than to find an individual bogged down in the length of life, devoid of the breadth.
[Sermon (1959), "Dimensions of a Complete Life," The Measure of a Man]

But don’t stop here. It’s dangerous to stop with the length of life. And some people never get beyond this first dimension; they live life as if nobody else lived in the world but themselves. And other people become mere steps by which they climb to their personal ends and ambitions. And if they manage to get around to loving, it becomes a utilitarian love; they love only those people that they can use. My friends, I say to you this morning that there is nothing more tragic than to see an individual bogged down in the length of life, devoid of the breadth. And so we must add breadth to length.
[Sermon (1960-02-28), "The Three Dimensions of a Complete Life," Friendship Baptist Church, Pasadena, California]

We must not stop here. It’s dangerous to stop with the length of life. Some people never get beyond this first dimension of life, they’re often brilliant people. They develop their inner powers. They do extraordinarily well in their fields of endeavor. They live life as if nobody else lived in the world but themselves. Other people become mere means by which they climb to their personal ends or their personal ambitions. Their love is only a utilitarian love. There is nothing more tragic in life to find an individual bogged down in the length of life, devoid of the breadth.
[Sermon (1960-12-11), "The Three Dimensions of a Complete Life," Unitarian Church, Germantown, Pennsylvania]

Some people never get beyond this first dimension. They may be brilliant people who superbly develop their inner powers, but they are shackled by the chains of a paralyzing self-centeredness. They live within the narrow confines of their personal ambitions and desires. What is more tragic than to find an individual who is bogged down in the length of life devoid of breadth?
[Sermon (1963), "Three Dimensions of a Complete Life," "2. Breadth," Strength to Love, ch. 9]

Now, don't stop here, though. You know a lot of people get no further in life than the length. They develop their powers, they do their jobs well. But you know. they try to live as if nobody else lives in the world but themselves, and they use everybody as mere tools to get to where they're going. They don't love anybody but themselves, and the only kind of love they really have for other people is utilitarian love, you know, they just love people that they can use. A lot of people never get beyond the first dimension of life. They use other people as mere steps to which or by which they can climb to their goals and their ambitions. These people don't work out well in life.
[Sermon (1967-04-09), "The Three Dimensions of a Complete Life," New Covenant Baptist Church, Chicago (audio)]