Asklemmy

This sounds more like you not really being aware of your qualities, and/or you looking at females who would not be a match for you (meaning neither of you would be satisfied if you tried). While there do exist qualities which make people truely unattractive (disorders such as uncontrolled rage for example), you don't say that.
It's true that mating choice in humans is foremost the female's choice, yet you might be surprised by what they see as qualities to appreciate. If you are an introvert, despair not, because 30-ish percent of all people could be classified as such, and that specifically could be seen as an appreciable quality by a woman who also sees herself as such ...

You are only invisible if you literally hide away. -- You do not give us much information as to why you think this way, or about your cultural background. You might be truely physically impaired or clinically depressive, or part of a culture where men and women are mostly kept separated, and that would actually make it more difficult but not impossible at all to find a match. Not having such information, i will refrain myself from just telling you to "go out of your hole more, man" and such. --

May we perhaps get a hint at your age? Because answers could get more helpful if we knew. (Don't ever think you are too old)

Yet, in whatever way you are set up, think of it like this: there are likely, literally, millions of people in your area and half of them are women, and a good percentage of those are in your age range (the older you get the wider this range gets). You can be certain that there is a sizeable number of women who have the same kind of thoghts and feelings as you do right now, and perhaps more important even, Your emotional and mental state can and will change.
In other words, you are certainly not unworthy in the eyes of the one you would not have expected to find you attractive. Of course, you need to actually show up in places where you likely meet people who share your interests (iow. "find you attractive") ...

My own experience: considered myself an "introvert" (until more recently i learned it's likely "more than just that"). Had great difficulties finding the right approach toward women in general, until i was 25 ... when it happened for the first time that a woman approached me, in a very assuring way (like, "want to come home with me, we make food and then I'd like to show you around my bedroom"). I took the chance and although i was "easy prey" for her it was the right thing to do because she was treating my inexperience in a sensitive way. Nevertheless, she was not a good match interest-wise, so that lasted only a couple of monts (and broke in anger).
A year later, a similar thing happened again ... at a seminar after-party, a student colleague who i wouldn't have thought of just so asked if she could stay the night with me. She didn't appear the most attractive to me but neither did i seem to be particularly attractive to others. Somehow i was wrong. That time it turned out quickly that it was me who was the more experienced one. ... And that woman was an "introvert" match (whom i now think of as being "more than just introvert", too) -- we've been a couple for seven years. ...
After that, both our paths in life changed considerably so we broke up in mutual agreement that we both needed to experience new things in life (i found a more spiritual-leaning path and learned what "love" is really about; she went with another man and discovered that she wanted to have children after all). ...

The relevant part here is that despite me thinking of myself not being particularly attractive, it kept happening that women just approached me, asking quite explicitly. -- And it almost always happened when i had gone into the company of like-minded people, but without the specific intent to seek out a woman. I can only remember one time when i did make an explicit move myself (even at that occasion i knew that i wouldn't get turned down because of the way she went all so lovely excited both times we had met before).
All in all, i wasn't together with very many and now that i'm older i still miss finding my true partner, but i can say that any of the experiences i got the chance to have, had its distinct flavour of enjoyability (well, perhaps minus the one time she later admitted she had abused me). Many of the women i love, i did never even get close to. A couple of times it was me who had to leave them behind because our paths just couldn't go together. A number of times it was sexual enjoyment for a number of days.

If you are asking, how does it feel ... well that's asking for poetry. Every experience is different though, and so will be yours (yes i say it will). It can be very satisfying, very lacking, questionable, exciting, soothing, mind-melting, enchanting, hurting, teaching. Pick yours. :-)