Ok:
High Rollers/Damp Hands or whatever is currently fashionable are the best tyres ever, for everyone.
No one needs a compact/triple.
Everyone needs tubeless/dropper posts.
Wider bars are always better.
Crank lengths don’t matter.
Mainstream bike brands are crap.
Oversimplification about frame materials.
And a particular favourite, no serious mtb’er would ride at night with a cheap light.
All examples of one size fits all tossery and ill informed opinion masquerading as fact.
What did Sheldon have to tell us about all these things?
Never really a fan of Sheldon’s site tbh, I’m sure it’s great for a roadie or anyone who hasn’t bought a bike part since 1990 but it’s just not often all that useful any more. And he was too keen on the old sweeping statement, which was fine at the time but means as things changed, his advice which was perfectly good at the time became less reliable.
Park Tools is much more useful IMO.
But a combination of some basic mechanical nous, and some skepticism, and google combined will fix most things now. Generally the crap advice is not hard to pick out, I think in the last few years I’ve only been caught out once.