We are just suggesting that it's not a good look. I don't think we should explain what constitutes a nice odd jacket everytime we say that, as there's plenty of info in the forum.
But to make things short, it looks like an orphaned suit jacket because it is solid grey, and has no rusticating features to help it look more like an odd jacket (patch pockets, throat latch, etc). Even if it did, it would need to be blue to look like a blazer.
If not dark blue/navy, odd jackets are better off with a pattern, preferably bold enough to distinguish it from a suit. Subtle patterns like a glen check with low contrast are common for suitings rather than odd jackets. Pinstripes and chalk stripes are usually suitings too. And worsted wool is usually reserved for suits, unless it comes in a bold pattern, wich could make a nice spring odd jacket.
In reality, it's much more complex than that (think camel hair odd coats, etc.) , but it's a good starting point. I learned through my own mistakes and being critiqued here, and I'm sure I still dress like crap - but at least I think I do have a much more solid foundation than when I first came here.
Thank for your advice.
The problem are probably the fotos I made. The colour is not grey it´s a light blue. Jacket has no solid pattern, it´s what we call in german "Pfauenauge" which means "peacock butterfly". I don´t know if that the right name in english. Here is a foto from the pattern and colour:
So thats why I think it´s a odd jacket and I react a little bit astonished when you call it "orphaned suit jacket".