I just read one from Miley Cyrus, quoting her dad Billy Ray Cyrus. “Never think outside the box, because there is no box.”
Similarly: you can’t reason someone out of a position they didn’t reason themselves into. (E.g. the futility of presenting facts & logic to someone clinging to an irrational position.)
Another favorite of mine: it takes all kinds to make a world. (Said when encountering someone strange.)
Be careful what you wish for; it might come true.
90% of what you fear won’t happen.
Don’t engage in a conflict unless there’s a good chance you will win. (I am paraphrasing Sun Tzu who said, “If fighting is sure to result in victory, than you must fight, even though the ruler forbid it; if fighting will not result in victory, then you must not fight even at the ruler’s bidding.”)
One I came up with: It’s better to look good than to be good. (This is said cynically, of course.)
When I was a kid, my father told me, " Never hit anyone in anger , unless you’re absolutely sure you can get away with it." ~Harold Ramis in “Stripes.”
Billy did it with a Spanish accent.
“It is better to look good than to feel good” isn’t a quote from Kim Kardashian—it’s a quote from Lorenzo Lamas’s father, Fernando Lamas, who was parodied by Billy Crystal during his time on Saturday Night Live.
Right. And not just hit… it’s applicable for pretty much any conflict. Case in point: someone at my workplace got in a major conflict with his supervisor and her supervisor. Even though he was “in the right,” his odds of success were very, very low due to politics, but he did it anyway. It ended up badly for him. Sun Tzu would have chastised him for engaging in a conflict when there was a low chance of him winning.
The lesson is not that you should never fight. The lesson is that you should not act on impulse, and you should make sure the odds are in your favor.
I remember one comic article where the writer quoted oppositional aphorisms. Like this:
I shouldn’t help you with the barbeque because “Too Many Cooks Spoil the Broth”.
Now help me clean up the picnic table because “Many Hands Make Light Work.”
And then there’s the so-called pyrrhic victory. You might win but at such a high cost that it isn’t worth fighting.
Wisdom from my mother: “Never pass up a good bathroom.”
If you find yourself in a fair fight, there has been a failure of planning or preparation.
At work:
Lack of planning on your part does not constitute an emergency on my part.
Might work in some personal scenarios…
I use this one all the time, now that I am getting older. Heh.
I like this one, and use it to keep myself calm when things don’t go as planned…
If a problem can be solved, there is nothing to worry about.
If a problem cannot be solved, then worrying will do no good.
Don’t sweat the small stuff.
To each his own ice cream cone.
You know what they say about sleeping dogs. You can’t believe a word they tell you. That’s okay, let 'em lie.
Speed kills!
Ah, a Tom Waits connoisseur 
Don’t sweat the petty things, and don’t pet the sweaty things.
From another board: “If you have a problem that can be solved by writing a check, you don’t have a problem, you have an expense.”
“We live among them every day, so we tend to lose track of just how strange humans really are.”
From one of my favourite blogs: “The only normal people are those you don’t know well.”
60% of anything is just showing up.
– Groucho Marx, IIRC