I was 9-0 in (not actually even important flex) placements and it was pretty terrifying since 10-0 is spicy.
Even if it was flex, and even if I knew I'd place plat 1 regardless of the outcome, it was pretty anxiety inducing. Still, I have to remind myself it's not going to get any easier if I play now or later, so just gotta click that play game button and not overthink stuff. (Alas, ended up 9-1, placed plat 1.)
I have another account with normals mmr that mostly matches with diamonds (unlike this account with is intentionally more like silver/gold normals mmr for ease of chests and learning new champs) which helps though. If I'm feeling in over my head with ranked, I can switch to that, go toe to toe with diamond+ players in a stress free environment to rebuild confidence, and then jump back on this account to beat my head against ranked again.
AFKs and autofilled players are frustrating as far as 'muh team' factors go, but faith in statistics helps there, so even if I have a rough streak of them, I have faith I'll benefit from just as many (or more) in the long term, just need to keep playing.