Imagine what the world would be like if the screw thread hadn't been invented. (That's just an example - it could just as well be something else that is similarly obvious-with-hindsight and is in everyday use, but it was screwing in wall anchors the other day that made me think of it.) The screw thread isn't really used much in nature (as far as I know) apart from on a very small scale so it is kind of plausible that somewhere out there there could be an alien species at a similar level of technology to us who just never thought of the concept of screw threads. It could be that (even despite having invented all sorts of other things) their minds are built in just such a way that the concept would never occur to them without having seen it. Maybe that when faced with the problem of converting linear motion into rotary motion, they use some other device (like the rack and pinion) or just somehow evade the problem altogether (by using nails instead, for example).
Now let's turn this hypothetical thought on its head and wonder if there could be some similarly simple and useful concept that we have just never thought of, that some alien species uses every day for all sorts of purposes. Some device that would easily solve all sorts of problems that we solve in much more complicated ways, just because nobody ever thought of the easy way of doing it. I imagine that when we do eventually make contact with intelligent alien species, that there will be all sorts of such "oh why didn't we think of that" moments (possibly on both sides, especially if it's a mutual first-contact situation). Probabably nothing as simple as the screw thread, but potentially all sorts of slightly more obscure things. Just one reason why the SETI project could pay big dividends if it is ever successful.