PostgreSQL is just better. It’s supports transactions on DDL (things like altering table structure) and enforces unique constraints after transactions complete … so you can actually do a bunch of important stuff (like update your table structure or swap unique values between rows) safely.
Eh… Without examples, I don’t know that this is a good warning.
Everyone gets into different technologies at their own pace. Even if it does bite OP in some abstract way because they eventually get to some complex use case, that’s okay; it’s all a learning experience.