Greg:
So, I will roll this your way: If you had malicious intent, what would be the worst watch advice you could give?
I have seen this advice given and seen this applied by collectors to themselves: only have one watch per manufacturer in a collection. Why would we ever limit ourselves thusly? Why would you ever think that is helpful advice to give to another collector/enthusiast?
Let’s say that you like a Seiko Alpinist (you shouldn’t, but that’s a discussion for another day). You buy one and enjoy it. You play with the internal bezel and like the modern touches like the cathedral handset. A few years later, when you are in the market or mood for a dive watch in a certain price range you immediately rule out all Seiko because, well you already have one and one is the limit. Really?
We are all drawn to certain brands because they have a consistent design language. There are similarities across the Omega range, or Rolex, or Orient. Despite the similarities it is not a stretch to say that someone who likes an Aqua Terra might also really enjoy a Speedmaster. They are plenty different. Why have such an odd arbitrary rule? I understand the need to diversify, but at what cost? I can avoid having seventy-five G-Shocks without such a rule.
If I wanted to destroy the enjoyment of owning too many watches, I would insist on only having one per manufacturer.
Chris:
I suppose if I wanted to be #evil, I would probably stop giving earnest advice from my experience and just say “go for it” to every question asked.
Vintage? Sure thing, don’t read my guide and dive in.
What about vintage digital? Go for it.
Electronic watches? Do it.
Rare vintage complications? Absolutely, the rarer the better.
What about (insert watch with pin-pallet movement here)? Buy that now!
The amount of damage that could cause is potentially catastrophic. If I ruin watches for someone then that’s a job well done. Go me.

Kaysia:
Worst advice: “Keep saving for your grail!”
Terrible advice.
Saving for a grail usually means years of abstinence from buying other watches, and I can’t imagine a worse idea.
Denying yourself the joy and experience of possibly hundreds of other watches while you doggedly squirrel away the pennies for a watch that I can pretty much guarantee will NOT live up to your expectations after all that time.
Why would you do that to yourself??
Every time you pass on a watch purchase with the thought “It’ll all be worth it when I get my grail.” you’ll be adding ridiculous pressure to yourself to love this grail. So when you do actually pick it up and it doesn’t fulfill all your heart’s desires like you have imagined it will (because it won’t, because it’s only a watch)…. it’ll be a sad day for you.
You’ll either have to suffer through the sinking feeling of all the wasted watch collecting time or turn repeatedly to social media with your new wrist shots in the hope that if enough people tell you how amazing it is you’ll start to believe it yourself.
Greg:
Vintage chronographs are a bargain.
Everything looks better on a NATO strap.
Sure, you can wear a G-Shock with a suit.
Lug overhang is a myth.

You must match your metals.
A true dress watch has only two hands.
Trusting your next watch purchase to random commenters on a watch forum is a good idea.
Did I miss anything?
Kaysia:
I’ll add…
Less than 36mm is a ladies’ watch.
Fashion watches are only acceptable as an ‘entry to the hobby’.
Quartz isn’t luxury.
You must climb the invisible watch ladder to luxury and beyond.
And if course… Don’t buy a homage, it will never feel as good as the original.

(I call this pastel “Homage Enthusiast.”)
Chris:
Ooft… this is getting brutal.
In line with my previous input, to all of it: “Go For It.”