The common assumption is that a fast site means an expensive server and complicated optimisation. In practice, most slow sites are slow because a great deal was added to them that nobody actually wanted.
A slider nobody scrolls to the end of. Three fonts, two of which are indistinguishable. A library pulled in for one small animation, weighing ninety kilobytes. None of these is a disaster alone; together they cost two seconds.
Why those two seconds matter
Because a visitor does not wait to discover how good your site is. If the page is slow, they are gone before seeing any of it — and everything you spent to be found is wasted at that exact moment.
Look at how quickly this page appeared. That is one example you can check yourself.
The route to speed is usually subtraction, not addition: fewer fonts, fewer libraries, images at the size they are shown, and pages built in advance rather than assembled on request. None of this is expensive. It only requires deciding.