It can get arcane getting the right socket mobo for your processor, getting the correct timings on the RAM, figuring out how much power supply you need to buy...
And then there's those poorly documented nonstandardized fiddly little wire connectors for all of the front panel functions, plus another set for the USB ports and so on. To this day I'm never sure which way to plug in the LEDs, and even when I think I have it down I'll run into a mobo that does it the opposite way. And then your case has a three pin power switch (outer two wired up), but the motherboard only has two pins for it...
I think your comment is, what, a decade out of date?
First of all, pcpartpicker and logicalincrements will help you choosing the right CPU with the right motherboard. Correct timings on RAM hasn't been a thing for many, many years, they work, at worst it won't use the maximum possibility the module offers. The PSU is hardly a problem, unless you are spending an extraordinary amount of money, the smallest PSU you can realistically buy is an overkill (CPU is 65W typically, very few GPUs go above 150W, and you can't even get a below 350W PSU really unless you have some office prebuilt from HP or Dell).
And then there's those poorly documented nonstandardized fiddly little wire connectors for all of the front panel functions, plus another set for the USB ports and so on. To this day I'm never sure which way to plug in the LEDs, and even when I think I have it down I'll run into a mobo that does it the opposite way. And then your case has a three pin power switch (outer two wired up), but the motherboard only has two pins for it...