Eventual Consistency
A guarantee that replicas will converge to the same value if updates stop, with no bound on how long reads may be stale.
The weakest useful consistency model, and the one most distributed data stores default to. It buys availability and low latency; it costs the ability to reason about a read.
The practical problems are rarely about eventual convergence and almost always about the window. A user who updates their profile and immediately sees the old value has hit it. The usual fixes are targeted rather than global: read-your-writes consistency for the writing session, monotonic reads to stop time going backwards, or routing a specific read to the primary.
Where it is genuinely unsafe is any read that gates a decision with financial or safety consequence. Checking a balance before allowing a withdrawal is not a place for a stale read.