When we need or want something that is necessary to satisfy our desires we need to document/explain clearly what the requirements are (in detail).

Providing a high-level objective can define what you are trying to achieve, but as often stated the devil can be in the details.  High-level requirements might get you started but without more detail, the results might not be to your liking.

For Example

You might engage a builder to construct a custom home for you.  The objective is simply stated to build a single-family home on this empty lot that conforms to the building code.

Without much more detail than that you could get a home that does not conform to your needs.  How many floors will there be, how many bathrooms, what color will the walls be and the list goes on.

In this example, the requirements can be quite straight forward coming from a single source, the homeowner.  There are many other cases where the evolution of the requirements can be much more complex.

Building Software

In the information technology space, application software development is a good example of a more complex requirements management  process.

Often there are many end-users of the software product and each may have an individual requirement some of which are contradictory.  Many of which are confusing and almost never with enough detail.

The cost or feasibility to provide all the desired requirements might be prohibabtive or for the sake of expediency.   Additionally because detail is often not provided or clarification sought the final software often does not meet the requirements.

If you expect to receive what you wanted clarity and detail is required.