Borrowing is OK so long as you can pay it back

This is a very specific manifestation of the 'Let's worry about that another day' principle. And this is a very expensive version. It's true that you can always find money if your desperate. Trouble is, the more desperate you are, the more it will cost you. The whole point about loans- from banks ,venture capitalists, loans sharks, credit cards or anyone else- is that they make money out of lending to you because you pay interest. That means you end up having to pay back even more, and if you haven't  got the money now, how are you going to repay even more then you've gained by borrowing? The more desperate you are, the harder it becomes to find a legitimate lender, and the more likely that you'll have to resort to a less scrupulous source, which will cost you even more. So don't do it.

If  you can't afford whatever it is- a car, furniture, clothes, evenings out, a holiday- then go without until you can afford it. The short term benefits won't be worth the spiralling misery of debt. And debt always spirals- the interest grows, you have to borrow more to pay off the original debt, you need another loan because it's getting harder to cover your everyday costs. And that horrible sinking in the pit of your stomach just gets worst every time.

Of course, not everyone who takes out a loan ends up in debtors gaol. But even you if you do successfully pay it back, it still costs you money. When it's all payed back, you have less than you'd have if you hadn't borrowed in the first place. So  it just make no sense. However tough thing are, don't borrow money unless you genuinely can't eat or have no roof over your head.