Forget “fair”. Most of life is not fair. Everyone does not get the same opportunities, have the same talent, or have the same luck.
Most singers will eventually find a way to mess things up. Some of us mess things up daily. Many of us go through periods where we feel like practicing is a performance of the “What the Hell Am I Doing Show”. I had a wonderful teacher who used to say “It’s a shit-storm in there.” while pointing to his head. He said that occasionally he would tell a singer not to practice on their own for a while, due to their boundless creativity for doing unproductive things in the practice room.
You are in your practice session, and things feel and sound wrong. Can you admit when things stink? “Oh my, this is really sub-optimal!” or for you earthy folks “Shit! Now what?!” Good. Now you are ready to address how to make things better. First of all, be kind to yourself. Laugh, even! Get mad if you must, but see if you can look at how ridiculous being mad looks. Or, backwards – you can get mad about how you are giggling at yourself. Both will get you to see the absurdity of it all. Ask yourself “If I was observing myself through a secret camera, how would this look?” Such ideas will get your Ridiculousness Awareness Threshhold (RAT) up. A mixture of exasperation and forced humor is not a bad place to start. Thinking everything is fine when part of you knows it is not, might get you through a performance, but it won’t hold up long-term.
At my age, after 50 years of practicing practicing, I have developed a very high RAT. I almost never get truly angry at myself when practicing anymore. I have learned to laugh, mostly by wanting to learn to laugh. Everything we do is fairly arbitrary and ridiculous when looked at from the “aliens observing earthlings” point of view.
As you have successes with warming up, working out, fixing problems, finding good people to help you, and implementing alternative strategies, you will more consistently believe yourself when you say “I will need to do something different just now in order to suck less.” And so you do.
Even if you are still making a mess, learning how to lighten up about the mess is essential. Unless you like being miserable. “Serious” is not just over-rated, it kills things.