So what could possibly be wrong with our understanding of it?
There are problems with Newton's theory, however. It doesn't quite describe the orbit of Mercury, the closest planet to the Sun, and as Newton knew very well it has nothing to say about what the force of gravity actually is.
It took over 200 years and the genius of Albert Einstein to discover a deeper theory.
Einstein's General Theory of Relativity describes the force we see as gravity as being due to the bending and curving of space and time (or to be more accurate "space-time") by heavy objects like the Earth and Sun.

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