The old-fashioned vibrators were pretty scary: Ten inches long with lifelike veins and made of a squishy, horrible material that made them alarmingly penislike ‑- except much bigger and much longer and much wider and ohmigod, is that what women really want? The answer is no. Then why were they created that way? Because those sex toys were designed by men ‑- men who, sadly, didn't have any idea of what turns women on.
Fast-forward to the 21st century: Now, most successful vibrator lines are heavily influenced by women ‑- and the first thing you'll notice is that most aren't even penis shaped. They're designed to stimulate the clitoris, which is outside the vagina, rather than for penetration. Yes, the "Rabbit," made famous by Sex and the City, is a firm favorite, but many women just turn it around to use the clitoral stimulator instead of inserting it.
The reason? Well, brace yourself guys, but only 20 to 30 percent of women can orgasm purely through penetration (without clitoral stimulation). In other words, your thrusting in and out alone probably isn't going to make the earth move for her. That means one of you usually has to use your fingers to stimulate the clitoris during intercourse, which is harder than it sounds. It's awkward: Your hand gets cramped, and it's hard to maintain the gentle, consistent pressure the clitoris needs when your hand is being pushed by the thrusting motion.