It didn't know enough to have faith in itself and its own future.

The result was the worries of others affected it to the extent of urging it to flee.

For the time being this enlarged its worries, until at length, falling in with a band of swans, it felt a strange thrill of fellowship with them in spite of their grand and beautiful appearance, and, soaring into the air after them, it alighted into the water, and seeing its own reflection, was filled with amazement and wonder to find itself no longer an ugly duckling but--a swan.
Many a mother, father, family generally, have worried over their ugly duckling until they have driven him, her, out into the world, only to find out later that their duckling was a swan.

And while it was good for the swan to find out its own nature, the points I wish to make are that there was no need for all the worry--it was the sign of ignorance, of a want of perception--and further, the swan would have developed in its home nest just as surely as it did out in the world, and would have been saved all the pain and distress its cruel family visited upon it.
There is still another story, which may as well be introduced here, as it applies to the unnecessary worry of parents about their young.

In this case, it was a hen that sat on a nest of eggs.