I think your YC bias is blinding you to the vast arena of companies different than those that would normally apply to YC. So it is more along the lines of 'YC essential start-up advices for the kind of companies that would apply to YC'. Not for start-ups in general.

• Launch now

This works, if your product is something that is trivial or extremely easy to manufacture. Many products are not at all like that.

• Build something people want

Which you may only find out during the iterating process.

• Do things that don’t scale

That depends. Almost all of the examples in the article are from companies that eventually scaled very well, and the 'do things that don't scale' advice is only applicable to some specific examples that held true in extremely narrow domains. For the most part start-ups are trying to find each and every kink in the machine to automate it as soon as they can so they can stay lean while growing. I'd change it to 'do things that don't scale and then find a way to scale them anyway'. The first part is just to get a feel for the problem space, the next is where you will end up making or breaking the company.

• Find the 90 / 10 solution

The Pareto Principle at work, can't disagree with that in any way, it is good advice no matter what the context. Perfection can wait.

• Find 10-100 customers who love your product

Some very successful companies have only 3 or 4 customers, you'd never hear of them because they are not sexy in any way but they are critical and usually have a lock in on their customers that most start-ups can only dream of.

• All startups are badly broken at some point

I'd change that to 'Almost all companies are badly broken in some way'. This is after looking at many of them over the years. That doesn't mean they can not function, merely that almost every company that I've ever looked at had one or more pretty serious defects.

• Write code – talk to users

Not all start-ups revolve around writing code, in fact the best of them when it comes to 'changing the world' probably do not.

• “It’s not your money”

See comment elsewhere, it's not yours either, it is the company's money.

• Growth is the result of a great product not the precursor

Growth by itself should not be a goal, and in many cases growth would be a problem. I've written this before, if growth was good then cancer would be good. So if you grow fine but be in control and aware of what parameters drive that growth and don't be afraid to step on the brake if it looks as if your growth is going to outstrip your capacity to deal with it.

• Don’t scale your team/product until you have built something people want

Sensible advice, regardless of what kind of company you run. Could be generalized to: "do not fall for the premature optimization trap".

• Valuation is not equal to success or even probability of success

I can't make much sense of company valuations in general and start-ups in particular, but I do know that even if the relationship does not hold in one direction, there does seem to be strong correlation between success in numbers and valuation.

• Avoid long negotiated deals with big customers if you can

That 'if you can' is instrumental, anything involving enterprise sales is going to have that element.

• Avoid big company corporate development queries – they will only waste time

True, but they are sometimes also ways to bankroll the company without dilution. I've seen a couple of successes happen this way and it seems like an elegant way to grow a company.

• Avoid conferences unless they are the best way to get customers

Agreed. Never went to a conference that I liked or that felt like time spent well.

• Pre-product market fit – do things that don’t scale: remain small/nimble

Remaining small and nimble is good advice at any stage. VCs that push you to increase your headcount should be avoided at all cost.

• Startups can only solve one problem well at any given time

Strong agreement there, this goes for almost all the businesses I've looked at. I'd even consider a start-up that tries to solve more than one thing at the time as being more at risk than any of their competitors solving only one of those. You'd have to be very good at everything in order to change along more than one axis in more than an incremental fashion.

• Founder relationships matter more than you think

Again, strong agree. I've seen more start-ups tank or lose momentum because of founder issues than for any other reason or set of reasons combined.

• Sometimes you need to fire your customers (they might be killing you)

But don't do it too early, make sure you drop them when you can afford to.

• Ignore your competitors, you will more likely die of suicide than murder

That depends, there is one situation where being unaware of your competitors can be costly: If one of your competitors has picked up funding and they enter your market with a price war or giveaway when you are still selling your product. This makes keeping a cursory eye on your competitors a good investment as long as it does not occupy you or one of your colleagues more than an hour or so in a month. It can also help to keep you 'feature complete' in the eyes of potential customers if you are going head-to-head in the same market, as well as to stay informed about their pricing and models.

• Most companies don’t die because they run out of money

I disagree with this one, not sure what your reason behind writing that so definitively was, but in fact the majority of companies dying are due to bankruptcy.

• Be nice! Or at least don’t be a jerk

Agreed. In the same line: don't burn your bridges.

• Get sleep and exercise – take care of yourself

That's good advice for everybody including those people that do not work on start-ups.

Thanks for posting all this by the way.