Why cash games annoy the shit out of me

To play poker you need the patience of a saint...
Aggression constantly needs to be tempered and it feels like a luckfest sometimes. Case in point tonight. I decide to fire up four $50 tables on Full Tilt, one deepstacked, so I'm sitting with $250 in play.
All good and in 90 mins I'm up $60.
One fold early doors hurt when I hit a set with 5s and folded to a potential str8 from the BB who could have had anything. Should have raised it up pre but decided to flat call. He carried on playing tightly so I figured it was a decent fold but it played on my mind.
I chipped away, played reasonably aggressively pre-flop, then hit a beauty set of 7s against an aggro-ish foe.
She played it well, slowplaying it, and won set over set, but the mindset of full-ring cash games, multitabling really has to be tight,tight,tight - prey on the weak, avoid the regulars. She put me all-in with a big reraise on the river and there is no way she would have played that way with two pair. It was a clear fold.
ABC poker, but it pays off.
A $50 win turned into a break even night.
I've now got that tight, hate poker, feeling in my chest which shows me its time for a break again.