PSU - The classic, don't cheap out on your power supply. Get as a minimum an 80+ bronze rated one fro ma reputable brand, I always recommend gold rating. Everything is connected to the PSU at the end of the day, if it's a shitty PSU, it can potentially fail in a violent way and damage other components.
MOTHERBOARD - This is a tricky one, because I have a personal experience with this one. It's funny cause currently there's a post on the front page asking what's the importance of the motherboard... I can assure you, it is important haha

This was the main problem with my first build, I just bought the cheapest motherboard I could find, like dirt cheap. It was an AsRock board.

I would get these awful frame drops while gaming, it was the motherboard overheating because I did not have any heat sinks (it had, but extremely small and ineffective) and it really wasn't made for that. I contacted the GPU manufacturer and they told me it was probably another piece in the build, after 6 months of frame drops I tracked down the problem, when AsRock support answered my mail: "That board wasn't made for heavy loads like that and it will not perform optimally if you play games" or something among those lines :(

The quality of your MOBO can affect stability of your CPU, RAM and others. Pick one that has multiple fan headers, a decent variety of ports on the IO, one with proper cooling, one that has the amount of RAM slots that you need, if you like listening to music maybe a good AMP is not a bad idea... you get my point.

See the MOBO as this giant PCB that you will be taking advantage of while you have your PC, think ahead!!! A MOBO can lasts you AGES if you plan your buy properly, you can upgrade literally everything on the computer and not have to change your MOBO because you really thought ahead.
source: reddit https://www.reddit.com/r/buildapc/comments/a0piyt/dont_cheap_out_on_the_psu_dont_cheap_out_on/