HOUSTON --Valentine's Day is meant for spending time with your sweetie or maybe searching for your soul mate. But did you know there's a secret to pursuing the perfect mate? We're taking closer look at birth order and how it may hold the key to your relationship success. Neil Armstrong made history when he was the first man to walk on the moon. No doubt Armstrong worked hard, but another first in Armstrong's life was a factor in his success. "Of the first 23 astronauts into outer-space, 21 first-born children," psychologist and New York Times best-selling author Dr. Kevin Leman said. In Leman's latest edition of super-popular "The Birth Order Book," he explains why the kid you were has a lot to do with the adult you are. First-born and only children lead the pack in life. Almost every U.S. president was a first or only. "The first-borns models in life are adults and that's why they become so anal, so determined, and so successful," he said. If you're an only child, just take everything Leman said about the first born and put a "very" in front of it. "Onlies" are like super first-borns. Frank Sinatra, former Secretary of State Condoleezza Rice and seven-time Tour de France winner Lance Armstrong are all only children. If you're a middle child, you may have already noticed -- you and that first born sibling are nothing alike -- and you're probably far more laid-back. "If the first-born's little Judge Judy and got an attitude, the second one's a manatee, just floatin' down the river," Leman said. That doesn't mean you're not successful. On the contrary, Donald Trump, Bill Gates and Steve Forbes are all middle children. Middles are the great negotiators. Richard Nixon, one of the only middle children to make it to the white house, and he brokered an unprecedented relationship with China. "They negotiated for everything they ever had in life," Leman said. "They never had mom or dad to themselves." And then, there's the baby, the life of the party who loves to make people laugh and knows exactly how to do it. "They're the little entertainers. They're the attention-getters," he said. "These people are tremendous in sales. They could sell dead rats for a living. They never met a stranger, they know how to get along with people and around people." There are many exceptions to the birth order rule. For example, if you are the first of your sex in the family, you're a first-born personality, and if there's a big gap between siblings, the birth order pretty much starts over. Also, if you had step-siblings, that blended family influenced your birth-order personality. If you're looking for love, birth order can help. The formula is simple. Just look for your opposite. "Only child and baby. First born and baby. First born or only with a middle. Middles are like going down to the blood bank, 'cause they find the universal donor. God bless 'em, they go with everybody," Leman said. You are by no means doomed if you and your mate have the same birth order. Those picky onlies are attracted to first-borns because they're so alike. "You just have to have a good division of labor," Leman said. Same goes for two babies. If you were the baby girl growing up and your boyfriend was also a baby, the two of you might throw a pretty big tantrum when you have to share the spotlight. So Leman says just knowing about birth order can help you see why that happens and keep those romantic sparks from turning into a grease fire.