They like to think they know what they're doing, but honestly, they have no idea.
Take Harry Kim for example (no, not *that* way...well...you can if you want). Intelligent, assigned to bridge duty on Voyager straight out the academy which obviously means one of two things:
1)He's immediate command material, or
2)His parents know some people.
Now, I like Harry. But I tend to disagree with the first option. The reason I doubt this is he complete inability to act normally about about any female he finds attractive.
You need some evidence? I'll tell you about our first (and I should add last) date. I knew Tom had set us up together, mainly because he wanted to get together with Jenny. Men. But, Harry is cute so I agreed.
Harry and I went to Venice on the holodeck together. A nice little trip in a gondola. He was clearly nervous, and I could tell he wasn't really going for it. Poor guy was still desperately in love with his girlfriend back home (Libby, I think her name is) and was only going on the date with me because of the pressure Tom was putting him under. I would have been insulted if I hadn't known that he was so nervous. Yes, he found me attractive but he wasn't attracted to me. And I have to admit that in some ways his 'innocence' was attractive to me. There's something erotic about teaching someone with such limited experience.
But...he blew it, not that anything would have really happened anyway. He finally found the courage to lean over to try and get a kiss...but his shaky movements rocked the boat and he soon found himself in the water! Oh that was hilarious! I can't tell you how much Jenny and I laughed about that when I told her. And after that I couldn't see him as anything but a nervous kid.
Still, that was four years ago. He's certainly grown up some since then and I'm happy for him. He's finally got over Libby, but now he's interested in Seven of Nine. Some part of me can't blame him. She certainly is gorgeous, and he seems to be the only one who notices! There's a big problem with that possible relationship though - she has no personality. If she can get over that arrogance then she'll be a wonderful addition to our little family. Jenny can't stand her, but she's never explained why.
And Harry's finally got some back bone. Well it's been there all along, but he was so timid about showing it.
So despite his development in that area, Harry just isn't someone I could get involved with.
Tom Paris however...well, that's really not my story to tell. I'll leave that for my sister.