Some proverbs are actively suspicious, like “Don’t judge a book by its cover” or “No pain, no gain.” Others have an opposite proverb that’s similarly common and reasonable.

• “Two heads are better than one” vs “Too many cooks spoil the broth”
• “Honesty is the best policy” vs “What they don’t know won’t hurt them”
• “Better safe than sorry” vs “Nothing ventured, nothing gained”

But the four below I use often:

1. The best defense is a good offense. This one even has a Wikipedia page that references Washington, Mao, Machiavelli, Sun Tzu, and “sports such as football and basketball” (citing a dead link to “diamondbackonline.com”). I can’t think of an opposite adage—maybe “prevention is better than cure.”
2. It's a dog-eat-dog world. This one isn’t true scientifically. “Two out of eleven dogs consistently refused to eat dog flesh. Eight dogs ate the raw flesh on more than half of the trials and five of these accepted it all of the time. All of the animals accepted the flesh after it had been cooked.” But metaphorically it’s often true because people are driven by self-interest. So often a situation lends itself to the remark that “it’s a dog-eat-dog world.”
3. The truth hurts! (Say this one the one the way Trump says “Sad!”) Often the truth does hurt. Maybe an opposite is “Ignorance is bliss” or “What you don’t know can’t hurt you” but these are less often useful principles. “The truth hurts” can be said often since a lot of cynical beliefs are true.
4. The people cry out for a strong leader. I don’t think this is a real adage but I often say it. It can be used in many situations where people lack agency because no one is giving them specific instructions on what to do.