In general, the airline won't let you get on the plane. If you are refused entry to a country upon arrival, it is the airline's responsibility to return you to your place of origin, so they have an interest in confirming that you hold the correct visa for your destination (if required).
Airlines frequently use a system called Timatic for this:
IATA Timatic is the industry standard used by airlines and travel agents to verify passengers travel document requirements for their destination and any transit points. Airlines use this information to ensure their customers are compliant with border control rules and regulations. Timatic delivers personalized information based on the passenger's destination, transit points, nationality, travel document, residence country etc.
It is your responsibility to make sure you have the required visa for your destination. The airline is unlikely to offer you a refund if you show up for departure with no visa.