Well, at the first glance, this Myth might actually be true… But…
It is never so simple to speak only about cost and effort.
Let’s take software development as main example (I am good at that).
If you are a company that does something unrelated to software development, such an approach might make more sense. But, there is “but”. 🙂
If you are a software development company, you need to go through the process of determining if you “build or buy“. “Buy” in this context means also to pay somebody to do it for you.
In any case, one thing has to be made clear: Never, ever, outsource something that is critical for your survival (e.g.: revenue, main product you sell, main system you use to do your job, etc.).
Since it is outsourced, you don’t have control on it. If the company decides to cancel the contract with you, or disappears from the market, you might lose everything.
Of course, there are all kind of contractual clauses, but anything that disrupts your activity is critical for your business.
So, “build or buy” careful…