toady I was trying to install Sierra on my 2015 MacBook Air and found something confusing. I made a bootable usb driver with Sierra and got to the macOS installer and erase the ssd of my MacBook in Mac OS Extended journaled and of course installed the Sierra on it. but after the process bar ended and reboot automatically it didn't go into the macOS setting screen where you can choose the location and language etc to set up your Mac. Instead it went to the macOS installer again? so I erased the hard drive again and installed and succeeded. and I found that the ssd was detected as pci ssd or whatever I can't remember when I went into the macOS installer the second time. I assume that is the reason why it failed? acutually I also came across this problem when I used windows laptop like 9 or 10 years ago. I always had to install windows twice to make it. what could be the reason?