Life is far from fair indeed - I have a deformed hip from a childhood illness that has caused me a lifetime of pain. I should probably have already had it replaced at an age that would be several decades younger than average for that surgery, but I'm too scared of the recovery and living with parts of my skeleton replaced by metal and plastic.

That said, I started a gym routine last year to try and relieve anxiety. I'm quite limited (you have no idea how much you use your hips until you get 8/10 pain for a few days after aggravating them). So it means low-impact activities and upper-body workouts. I didn't think it would make any difference in my appearance; I just needed to move in any way I could. After a few months I started getting comments about putting on muscle and overall looking better. (I lost of lot of weight which is more attributable to cleaning up my diet concurrently to a gym routine) A co-worker I met assumed I must be ex-military which I found funny because the childhood illness I had is specifically named in their document of medical exclusions. I don't think it's any secret that people treat you better when you appear more fit, and it is something that you have some control over.

But I don't believe that looks are motivation enough to get you to the gym every day (at least for me it is not); it's much better to do it for your well-being. Ideally, you can find exercises that both workaround your injuries and that you enjoy. Also, it's not like you need to go hard at the gym for two hours a day every day of the week; just do what you can and take pride in what you are able to achieve within your limits.

I've spent a lot of my life regretting my circumstances in unhealthy ways which I ultimately regret. I can't say that everything is wonderful now or even good, but they are better.

"with knee issues with which doctors can't help (just rest some, sure, like 8 months now since it began)."

Usually knee issues do not heal with resting, but with moving. And rather get worse over time while remaining passive (in resting position only some blood flows through the whole knee, and the muscle detoriates quickly and without a strong muscle, even more stress gets onto the knee)

So unless you have a very special condition where competent doctors especially said, only resting will help, rather get active again with light activity. Walking, cycling, dancing, climbing, ...

Every exercise that moves the body, without putting too much stress on it.

Competent doctor told to rest. Left knee MRT showed a "stress break" (don't know correct terminology in English). Problem is there has been no stress for last 6-7 months apart from time I was trying to start running (ironic). Either it doesn't heal for half a year or it's something else. I also had to wear this cloth knee support thing for a couole of weeks after some extra long walking with friends, as the knee didn't like any load at all.

It's not over yet, there will be excercise, waiting in line for a specialist, but not walking/cycling/dancing/climbing, execises you do at home when you have an injury.

Anyway, I tried to exercise, I got an injury, and I felt worse than without exercise, cause something was taken away from me.

"I also had to wear this cloth knee support thing for a couole of weeks after some extra long walking with friend"

My experience with bandages is, only use them when you absolutely have to. Otherwise your body gets used to them and sees even less need to make the knee work on its own.

In general, I am not a doctor, but went through years of working out how to fix bad knees and went from doctor to doctor, operation etc. (most doctors were actually very bad for anything not routine)

What helped in the end, was establishing a habit of doing special knee exercises whenever possible. And lots of adequate sport in moderation. Climbing and Trampolin may sound crazy, but are actually pretty good for the knees if done on a light level and also walking barefeet helped a lot. In general, trying to get the muscles around the knee as strong as possible, as then the muscles can hold your knee to replace whatever is broken inside your knee.

"Anyway, I tried to exercise, I got an injury, and I felt worse than without exercise, cause something was taken away from me."

And I would be careful with your conclusion, in my opinion you just did too much of wrong exercise. That is bad, yes (and is also what messed up my knees initially). So maybe try to find activities or exercises that are fun, but not too hard. And yes, it sucks not being able to do, what you could do before. At some point I allmost thought I would never be able to run again. And I definitely will never get back to the state of before - but I managed to do quite a lot again. Anyway, all the best for your recovery.