Kennedy acknowledges that the political and international challenges he has described cannot be solved quickly. By referring to one hundred days, one thousand days and even an entire lifetime, he rejects the idea that major public goals can be completed within a single electoral cycle or administration. Progress, in this view, may require sustained effort across generations.

The final phrase, ‘But let us begin’, shifts the emphasis from completion to responsibility. Kennedy argues that the scale or duration of a task is not a reason to postpone action. In the wider inaugural address, this applies to problems including war, poverty, tyranny and international cooperation. The quotation therefore combines realism about the limits of immediate political achievement with a call to act. Its broader message is that worthwhile public work can be justified even when those who begin it may not live to see its completion.