It took me a handful of rides to figure this out. I had a saddle which was hard plastic with a suede covering, but it was wide enough for me and I was reasonably comfortable on it. I rode my first century on that saddle, and a 3-day 100 km/day tour on that saddle ... plus a lot of other rides.

Then my father gave me a saddle which he had used and liked and thought it would work for me. My first ride lasted about 5 minutes. OW!! Thinking it was just me, and that my butt needed to get used to the new saddle, I tried again a few more times but it just wasn't working at all. Very painful.

So I went out and bought a new, wider saddle ... world of difference!!

Your saddle should be wide enough for your sitbones to sit comfortably on the saddle ... but of course not too wide. There's a happy medium.

But you have just stopped at the discovery that width matters. There's more to it. The shape of the saddle matters as well. I have tried both completely flat saddles and saddles that curve up in the back a bit, and have discovered that I need a saddle that curves up in the back a bit. All the saddles I own which are even somewhat comfortable curve up in the back, and when I tried flat saddles, I didn't feel like I was getting the support my back needed. The longest ride I tried on a flat saddle was 100 km, and my lower back was uncomfortable the whole way around. On a saddle that curves up in the back, my lower back is just fine.

And so, for me, the Brooks B17 works.