A few weeks ago, First Round Capital hosted its annual summer party in the Bay Area. The venue was trendy, the line to get in was long, and the conversation among the crowd of serial entrepreneurs and investors became predictable: Founders chatted not about their recent successes but about the next thing they wanted to do.

"I have the bug," one CEO told another over bass-thumping Rhianna. His mind was already on his next venture even though he was still in the process of closing the acquisition of his first.  

And that is exactly where most entrepreneurs go wrong, says Eric Jackson, a Forbes contributor and founder of Iron Fire Capital.

Silicon Valley entrepreneurs suffer from what social psychologists call the “fundamental attribution error,” Jackson wrote recently on his Forbes blog.

Without delving into the psycho-babble, the gist of it is this: Most people tend to overestimate their own abilities when they're successful and overestimate the role of circumstances when they fail. And so, if they've had one big hit they're confident there's always another great idea looming around the next start-up corner. If their brilliant idea flopped, well, maybe the timing just wasn't right?

Many Silicon Valley VCs, First Round included, expressly state that they are more interested in serial entrepreneurs with track records than first-timers. This, Jackson says, only intensifies the entrepreneurial “fundamental attribution error.”

“When you’re surrounded by so many other successful entrepreneurs in the Valley, success seems so close you can touch it,” Jackson writes. “But there’s another side to all the start-ups: lots of failures.” 

Just this week, Facebook CTO Bret Taylor announced he plans to leave the social network--he, too, has the start-up bug. But, according to Jackson, history says the first success will always be the biggest. For Taylor, that was FriendFeed. And the same goes for others: Even with the recent launch of AirTime, Sean Parker has had trouble matching his initial success with Napster. After entrepreneur and VC Mark Andreessen made it big with Netscape, which AOL acquired for $4 billion in 1999, he followed up with Loudcloud and Ning--but neither matched the success of his first blockbuster. YouTube co-founders Steve Chen and Chad Hurley have also been struggling to find their next “big” idea after selling to Google in 2005.

Not quite everyone fits Jackson's Silicon Valley psychological diagnosis. He says look no further than Mark Zuckerberg to see an entrepreneur who's acutely aware of his limits.

“You just saw my apartment,” Zuckerberg told then-president of MTV Michael Woods in 2005 when he asked why he wouldn’t sell Facebook to Viacom. “I don’t really need any money. And anyway, I don’t think I’m ever going to have an idea this good again.”

Humble, and, probably right.