It would be great to have a truly passive income — you work on something once and then it keeps generating money forever. But that’s of course not the case. Passive income is never truly completely passive. However, it’s almost passive. That’s still good — it keeps generating income while you sleep — but it does require some maintenance every now and then.
My brother and I made a few games. They are being sold on Steam. Every day a few people buy them. And so we keep getting paid even though we are not actively working on them anymore. But sometimes there’s an elusive bug that someone reports, and we need to fix it. Or people keep requesting new translations. Sure, we can not respond, but it’s better to patch and update the game so that players are happy.
Same with an apparel store. You could make a lot of designs and add them to your Threadless or TeePublic shop and you will keep earning money. But there are things you should do if you want to maintain the same level of profits. For example, suddenly people start searching for specific themes like, say, “social distancing”, so you could check which of your designs can be tagged with those keywords. Or new products or colors are added and you should enable them in your shop.
In fact, Threadless has just added new products for all Artist Shops — Classic Fleece Pullovers and Hoodies. So if you have a shop, you could go there now and enable your designs on those new products. It’s worth your time because the classic fleece colors are very nice, I think they will sell well. If you are unsure how to enable those products I wrote a mini-tutorial. And Threadless wrote a blog post about it, too.