Nobody has ever thought "this site is taking a while, I'll wait." They go back and click the next result. You never find out it happened, because the person who left doesn't fill in a form to tell you.
Speed is the one thing about a website you can judge without knowing anything technical. You already know what a slow site feels like. The useful question is whether yours is one of them, and most owners have genuinely no idea, because of how they test it.
You are the worst person to judge your own site
You visit your site from the same phone, on the same wifi, several times a week. Your browser has already saved most of it. So it loads instantly for you and slowly for a stranger on mobile data outside a supermarket, which is the person who actually matters.
Two ways to check properly:
Open your site on your phone, on mobile data rather than wifi, in a private window. That clears the saved copy and gives you roughly what a first-time visitor gets.
Or hand your phone to someone who has never seen it and watch them without helping. You'll learn more in ninety seconds than from any report.
What usually causes it
In order of how often we find it:
Enormous images. Someone uploaded a photo straight off a camera, so the site is sending an 8MB image to a phone that needs about 200KB of it. This is the single most common cause and the easiest to fix.
Too many add-ons. Chat widget, cookie banner, booking tool, three tracking scripts, a review widget, a font loader. Each one is a small delay. Together they're the whole problem. Most sites are carrying at least two nobody remembers installing.
Cheap hosting. The server takes a second or two to even start answering. Nothing you do to the page fixes this, and it's usually a $10-a-month problem masquerading as a design problem.
A page-builder theme. The kind sold with forty demo layouts built in. You use one. The site loads code for all forty.
The part that sneaks up on you
Google has used speed as a ranking signal for years. That's real, but it's secondary, and people over-index on it because it sounds technical.
The bigger cost is the one you can't see. If your site takes six seconds and a competitor's takes one, you don't just lose the impatient people. You lose the comparison. They saw both, one felt like a real company, and yours felt like it might not still be trading.
What "fast enough" actually means
You don't need a perfect score. Chasing a green number in a testing tool is a good way to spend money on nothing.
What you need is for the page to be readable in under about two and a half seconds on a phone, on mobile data, and for it to stop moving once it's there. Text that jumps around while images load is worse than a slow page, because people tap the wrong thing and give up.
Get those two right and you're ahead of most of your competition. The rest is diminishing returns, and there are usually better places to spend the money.