I'm a guy I can honestly say I don't have a very big penis. Last time I measured it I was 15 and back then it was 5.9 inches, I have no idea what it is now though. But from my experience foreplay is what has decided whether I get to penetrate or not.
I ate a girl out once and stimulated her entire body for like 30 minutes to 1 hour and she orgasmed what she told me was 3 times. She was so dizzy and horny that she simply stared into my eyes and literally begged for me to put it in, she didn't even look at my penis because that's how much she wanted it and she didn't care how big or small it was.
And for those of you who'll say "omg ttat dident hapen u lier" I'll just clarify that this did indeed happen, I'm using my experience with this girl who happens to be my girlfriend today to show you that foreplay plays a very big part. I do my very best to sexually stimulate my girlfriend before penetration so she's at her peak once I do penetrate. While my girlfriend is the kind of girl who prefers bigger penises (7-8 inches, she told me herself) she is enormously pleased with both me and my penis simply because I stimulate her so well before I penetrate.
Some ignorant guys think sex starts once they penetrate but that's not true. Sex starts after you've gotten undressed and lie down in bed together. Stimulate your woman!
Women, please don't tell men their penis is small even if that's what you think, it can cause some major emotional trauma and insecurity which can potentially lead to erectile dysfunction (speaking from experience here). Or worse, they may not be able to get it up at all. Some men need professional help to cure this condition which can be so easily avoided by being considerate.
That's the kind of effect it has on men. It may not happen to all men, but for those who are already dissatisfied with their size it's like pouring salt on the wound. It may not seem like a big deal to you but to men it is.
But enough of my rant.
As a guy I can say I'm slightly dissatisfied with my penis size, but at the same time I try to think I'm born this way and I can't change that so I've learned to accept me for who I am, penis and all. I was lucky enough to find an amazing girl who is not only a magnificent lover, but also beautiful and a very wonderful person. We have sex at least once per day.