A lot of the time, when people say "let's be realistic", it tends to sound as if the only things that exist are the things that are possible right now, and we shouldn't entertain ourselves with big goals that are unlikely to happen. It can be short-sighted, cowardly and not realistic at all - after all, reality contains possibilities, so if you dismiss them outright, that's a warped view of the world as well.
A lot of people like to brand themselves as 'realistic, practical' people, but when I see the actions they take, it doesn't seem to look like it.
In fact, sometimes the practical thing to do may be the riskier or the more unknown thing. Have you heard of the term expected value? If the chances of something happening is really small, but you get a super huge payoff, then the expected value of it could still be fairly large.
An example: a stable job paying $4000 a month, or a blog that might make $10,000 a month? If you think that your chances of the blog happening is about 40%, then logically they're basically the same options in terms of payoff (10,000 x 40% = 4000). Or, if you think you can get an even larger payoff, then rationally you should pick the latter option.
You can choose the former, too, but you can't say that the latter is impractical. After all, you get the same value from it. Only seeing the negative side of things doesn't make you realistic; it's just as bad as being overly optimistic.
Sometimes "being realistic" is used in the sense that people are all self-interested, and so you should only care for yourself and your immediate family. Chinese families like to do this - one of the reasons they have kids is so that they have someone to pass their assets to. But if, in the accumulation of these assets, we damage the value of the future, then we actually cause these assets to depreciate. How does that make any sense?
I'd say being selfish is actually harmful and not the path to take if you are rational. When you look at businesses, the ones that work out are the ones that collaborate - even selling to customers require collaboration. And, our selfishness has probably threatened the longevity of humans as a species, which is actually not rational, either. If you are self-interested, then you must care for the interest of others, because then you can maximise your own overall gain, too. Working together beats wasting resources competing against each other, and we can improve as a whole.
I think there is a better way to go about doing things. See practicality and realism as a tool that comes in during the planning stage, not the ideation stage. Also, see it as a long-term thing; if what you want to do makes sense across years and decades and centuries, then do it. Otherwise, it probably only seems 'practical' in the short run.
And remember: dreams can happen with a plan, but plans don't even get made without dreams.