Very true. I have 40 or so domains, but none were purchased as an investment. All because of some random idea I had. Always happy to sell them for totally reasonable prices.
Edit: For example: 2 years @ $10/yr so I sell it for $20.
I do have one exception, and that is I bought sms.me which I had planned on building, but I got a good offer so that sold for many thousands, but that was their offer not mine.
On the flip side, I've bought many domains that I want to use for products ranging from $100 - $30,000 depending on a number of factors.