In practice
The three metrics cover how quickly the main content renders, how responsive the page is to input, and how much the layout shifts while loading.
Most failures come from the same short list: unoptimised images, blocking fonts, and third-party scripts nobody owns. Fixing them is engineering work, not a plugin.
Why it matters
They are a small ranking factor and a large conversion factor. Faster pages convert better regardless of what search engines do with the signal.
Related terms