Most that are "scary how accurate they are" are really just saying stuff most people would agree with. Look at these ones from different sites for me (Pisces), with my notes:

Astrology.com:
You've got an altruistic streak that goes deep, and right now it's showing the world how people should treat each other. Follow your instincts and don't worry about how things are going to be tomorrow.

<font color="red">I'm actually not that altruistic, but a LOT of people would consider themselves so. They'd read this and think, Wow! That's true about me, so I should follow the advice. But the advice is just generally good advice...for anyone.</font>

Horoscope.com:
You’ll experience a surplus of Fire energy today which will be heightened by the position of your ruling planet, Jupiter. Decisions that don’t usually faze you will seem harder today, and you might even find that you’re a little irritable too! Don’t worry though; this will ease over the next few days.

<font color="red">I don't really know about the meaning of planets and positions and all that, so I won't address it. But the first part, about decisions. Normally, each day, we have easy decisions and difficult decisions. But a person who wants to believe this info (or who is prone to not thinking beyond what's in front of them) will think, hey, yeah, some of the decisions I've had today were harder than usual, even though I don't usually have trouble with them. And decisions that are difficult can irritate us, so that wouldn't be unexpected. Plus, if you had anything at all cause you the smallest amount of irritation, you might take that to "prove" this horoscope was accurate.</font>

Horoscopes.com:
Back to the simple things. Today, simplicity is your key to having the most successful and satisfying day. That means you'll want to avoid situations that seem overly complex. Instead, choose to do things in the simplest manner possible. It's also a great day to focus your time on favorite places, activities and people.

<font color="red">The above could be applied to any day!</font>

When somebody gives me a horoscope or a prediction that is very specific and not generalized, I might give it some consideration.