MenHealth.com writes:
Simply put, confidence gets the girl.
In Learn How You Can Get A Great Girlfriend on the blog DatingPaladin the author writes:
Getting a girlfriend is something that all straight guys want. [...] Confidence is the most important thing for getting girls.
The belief that man have to be confident to get in sexual relationships seems to be very popular on the internet.
Is there psychological research that proves that confident guys are less likely to be single than shy guys?
This isn't exactly to my satisfaction on scientificalness of approach, but the best numbers I was able to find so far come out of this:
Match.com, which helped to pioneer the online dating industry, has revealed the results of its Singles in America: 2013 survey. More than 5,000 single men and women 18 and older participated in the survey. Here are some of the findings:
92% of single men feel comfortable if/when a woman asks them out
The "big three" criteria by which singles judge a date are grammar (83%), confidence (78%) and teeth (76%)
Elsewhere in that survey, it was mentioned that 83% of men wanted a confident woman, which means that the above generic 78% (assuming 50/50 survey response breakdown) would imply ~73% of women prefer confident men.
Obviously, this suffers from faults (self selection bias, demographics bias, bias of people pressured to respond to make a favourable opinion of themselves, as well as some assumptions outlined above). But it's the best I could find, and seems to indicate that confidence in a man is a pretty important factor as stated by Match.com responders.
Another possible fault of this survey (but it would be inherent in almost all sources using what people say vs. what they do) is that there may very well be a large discrepancy between revealed and stated preferences, that would be impossible to detect absent actual behavioral observation. (And even a behavioral observation would not necessarily be accurate unless done "in the wild", so to speak - without the pressure of being observed and judged by researchers).
There's no raw data available for the survey, but all the figures quoted above are found on their infographics/websites: http://blog.match.com/category/singles-in-america/ and http://www.singlesinamerica.com/
In Sexual Behavior, Sexual Attraction, and Sexual Identity in the United States: Data From the 2006–2008 National Survey of Family Growth from the CDC web site, Figure 1. Sexual behavior in lifetime among men and women aged 25–44 years: United States, 2006–2008 on page 9 claims that 97% of men have had vaginal intercourse with the opposite sex (and 90% oral sex with the opposite sex).
This data suggests that it's not just "confident" guys who "get the girl" but, rather, virtually all guys.
Similarly, table 2 on page 18 says that 1.2% of men aged 40-44 years have never had sexual contact with the opposite sex (nearly 80% of men in this age range have had exactly 1 female sexual partner in the last 12 months).
First, the question was about "likelyhood". Given that 98% of men "get the girl", then IMO the likelihood of a man having got the girl is about 98%. If the question had been about "getting 1000 girls" then I wouldn't have posted this answer. Also I was more-or-less ignoring the question-as-asked, and instead trying to give evidence related to the claim-as-quoted.