When I was a kid my older brother liked to work on cars/engines and always used Castrol. So when I got my first car that was the brand that I trusted as well. Used a lot of gtx and I have to admit that it never let me down (in the sense that I never lost an engine before the rest of the car was ready for scrap).
Later there was a real old mechanic that I used to take my car to. He didn't supply anything and would tell you what to bring - oil, coolant, plugs etc - whatever needed changing. He'd always say "and bring 5 liters of Castrol oil". Like always emphasize *Castrol*, so that kind of re-enforced my belief that it must be something special.
Then one day I brought in Valvoline (XLD) instead and I was kind of half expecting him to make a fuss about it not being the oil he asked for. Instead he just said: "ok, this will work fine too". So finally I asked him, so why do you always ask for Castrol oil then? He said it was just a brand he trusted because he'd used it for a long time. He admitted that there was nothing wrong with other brands, but he still preferred to stick with what had worked for him in the past.