To ensure candles don't fall out of holders, you need to secure them properly. This can be achieved by using a few simple techniques. One common method is to slightly melt the bottom of the candle with a lighter or match, then quickly place the candle in the holder while the wax is still soft and malleable. The melted wax will harden and act as a glue, keeping the candle firmly in place. Another technique is to use candle adhesive or sticky wax, which is specifically designed to hold candles in place. It's a safe and effective solution that can be easily applied to the base of the candle before placing it in the holder. Always remember to ensure that your candle is straight and centered in the holder to prevent it from tilting and causing a potential fire hazard.