Cloud providers secure the infrastructure underneath your workloads — the physical data centers, the hypervisors, the network backbone. What happens on top of that is on you. This split, usually called the shared responsibility model, is where most cloud breaches actually originate: not a flaw in AWS, Azure, or GCP itself, but a misconfiguration in how a business used it.
Publicly accessible storage is the most common and most avoidable mistake — a storage bucket or database left open to the internet, often unintentionally, exposing customer data or internal files to anyone who finds the URL. Automated scanners look for exactly this, constantly.
Overly broad identity and access permissions are a close second. It's common for service accounts and users to accumulate far more access than they need over time, simply because it's easier than scoping permissions precisely. That convenience becomes a liability the moment any one of those credentials is compromised.
Unencrypted data — both at rest and in transit — and unmonitored API keys are two more recurring patterns. Cloud providers make encryption straightforward to enable; the gap is usually that it wasn't turned on by default for every resource, not that it was hard to do.
A practical starting checklist: enable multi-factor authentication for every cloud console account, audit storage and database permissions quarterly at minimum, apply least-privilege to every service account, turn on encryption everywhere it's available, and enable your provider's native logging (CloudTrail, Azure Monitor, or equivalent) so you can actually see what changed and when. Most of this is configuration, not new tooling.