Let's suppose that you're photographing some basically human things. So, we're setting aside Landscapes, Abstracts, Still Lifes, Macro Photos of Bugs, and so on. This is a lot of stuff, to be sure. But let's suppose you're shooting Street, or Documentary, or something like that.
The essential hurdle photographers run in to here is People. Can you, or Can You Not, photograph people from up close and personal?
People have a sort of bubble around them, I imagine it shaped a bit like this:
The edges of the bubble are vague, the size and the fuzziness are personal and contextual. The point is that the closer you get to someone, the more likely you are to have to engage them socially. You can get closer from behind than from the front. As you approach, at some point there's a chance of eye contact, of registering your presence. At some point there's an obligation to acknowledge the other person. At some point someone's going to have to say "Hi" or risk a horrid awkward silence.
There is, for everyone, a cost associated with entering the bubble. It's going to take effort and energy. In the first place you either need to interact socially, or consciously thrust down that urge. In the second place, there is risk of rejection, of a negative social interaction. This is true, I think, for everyone. Except, perhaps, for sociopaths of a certain stripe. We're social animals, and this is part of that.
Some people can and do enter those bubbles constantly, other people never, ever, enter the bubble. The latter take a lot of pictures of people from behind, or in the distance. The latter will often have a line of patter about how they want to abstract the humanity of the scene or photograph something Universal rather than specific or whatever. And, sure, that could be a thing. Those are legit pictures too.
I have a hell of a hard time entering The Bubble myself. I'm socially competent, but not very gregarious. I'm an introvert, so these things consume quite a bit of energy.
But here's the rub. If you won't enter The Bubble, your camera isn't in The Bubble either. And that in turn means that people looking at your pictures are not in The Bubble. They're outside. People in the frame are beyond the boundary of social interaction, they are safely distant. They might be far away, they might be turned away, they might simply be distracted.
Be keeping yourself emotionally safe, by taking pictures from that safe emotional distance you make pictures which are -- duh! -- emotionally distant. It's baked in. You can't fake it. We're social animals, we know intimately, powerfully, when we're inside that emotional-engagement zone, and when we are not. A long lens is not going to make up for your timidity.
As a consequence of this the emotional palette of your pictures is limited. You can go all the way from "dystopian hell" to "neutral." If the scenes are of a sort in which we expect social things to occur, and there is nothing social in the pictures, it's going to feel off. If you simply leave people out, you're likely to end up with an "abandoned" vibe, although it's just as likely you simply waited for the moment when nobody was in-frame. If you photograph people from behind, or from a distance, it will feel anonymous, distant. Even a crowd can be photographed as distant, aloof, unsociable.
Suppose you want to photograph human scenes, pictures in which we expect some sort of social engagement. Suppose you want to project a positive mood. Well, you're going to need to get into some bubbles and engage some people. Your camera needs to be engaged, so the viewers of your pictures feel engaged.
Perhaps this is what what's-his-name (was it Capa?) meant when he said something about "If your pictures aren't good enough you're not close enough."