Have you ever hated the sound of your system one day, and loved it the next?

I had similar experiences regarding perceived SQ at different listening times...until I got serious about the setup and room treatment in my dedicated listening room. Made all the difference in the world.
The room will dictate half of what you hear.

This is normal. What you hear is subjective and will be heavily influenced by your mood and whether you have a cold, slept well or not etc.

Also much boutique equipment is finicky and very unreliable (like tubes).

This is probably the single biggest reason audiofools hear amazing things from fuses or ordinary bits of wire. The mood and expectation is extremely powerful in all humans. Foreplay is a good example. A finicky system that is on the fritz is yet another,

The trick is to recognize what is real from what is subjective and to restrict audio component purchases to reliable rather than boutique brands. Also avoid used gear that may have been damaged by misuse and non-qualified repairs. Those unable to do so are destined to keep buying new cables and performing countless new tweaks. The mind trick of the tweak creates the predisposition to feel more positive about the sound.

shadorne"The mood and expectation is extremely powerful in all humans. Foreplay is a good example.The trick is to recognize what is real from what is subjective."

Tell us more about your tricks shadorne.

@clearthink

A simple trick is to buy the same gear that is used by professionalslike Sting, Pink Floyd, Diana Krall and Mark Knopfler. Folks who make a very successful living from making music tend to demand good quality as well as good reliability. Just be careful of endorsements like Dr Dre and his headphones. Musicians that receive commissions or benefits for endorsements may not be giving their unbiased preference. For example, Daniel Craig 007 wears Omega when he goes out at a public function (sponsored) but privately he wears Rolex.

I have never felt there were changes from one moment to the next. I have had first Quad els57s and later Quad 2805 speakers, and they have always sounded the same from one day to the next. The 2805s were an improvement, but in the same family. After a while with the 2805s I decided I needed a more powerful amplifier than the Quad 303, so I acquired a refurbished Quad 606-2, and that was indeed better, but every single day, and not varying from one day to the next.
I do agree with Shadorne that buying gear that professionals also use is a good way to proceed. Tony Faulkner, the famous classical sound engineer, also uses Quad stats for his recordings. My small system uses Harbeth P3ESRs. The British Library’s sound archive uses Harbeth speakers for their recording and transcription work. Neither of them go for audiophile tweaks. They know better.