A Small Craft Advisory identifies conditions the NWS expects to be hazardous to small craft. The exact combination of wind and waves is provided in the message, so read the full product rather than relying on an icon.
A boat can be unsafe below advisory criteria when it is overloaded, underpowered, poorly maintained or operated by an inexperienced crew. Conversely, an advisory does not certify any particular vessel or operator for the conditions.
Use a conservative personal limit based on the vessel, route, daylight, crew and escape options. Delay the trip when uncertainty is high.