Which financial principle is essential for maintaining a charity's sustainability?

The principle of ensuring a steady flow of donations and endowments is critical for the sustainability of a charity. This is because charitable organizations often operate on limited budgets and rely heavily on the generosity of donors to fund their programs and services. A consistent inflow of donations allows the charity to budget effectively and plan for long-term projects without the immediate fear of financial instability.

Moreover, endowments can provide a source of funding that sustains the organization even in lean years. This financial support is essential for maintaining operations, supporting staff, and delivering services, which are vital to meeting the charity's mission. By focusing on building and maintaining a solid base of donor support, charities can ensure their ongoing viability in an ever-changing financial landscape.

The other options do not address the underlying need for consistent funding from contributions. Generating profit margins applies more to for-profit entities, maintaining ownership of all assets may not be relevant for a charity that needs to allocate resources efficiently, and relying solely on grants can lead to financial instability if those funds are not regularly secured. Therefore, the focus on securing donations and endowments stands out as the foundational aspect of a charity's financial sustainability.