But to the extent you do buy, it is nice to know.

For example, even for an open hardware design, you need to buy parts.

But some things are either possible, but already nicely packaged by someone else (my opengarage I could have built, but it was well worth it to buy). A video doorbell I don’t see good open designs for, so the “part” is the doorbell itself. A bed cooler has open designs, but they call on you to basically buy a donor commercial product to use for parts.