I saw a candle on the road. Why didn't it burn?

Because the cotton thread does not completely absorb wax oil as a wick.

Because the wick is the "transmission pipeline" of fuel, it must first soak the melted wax to absorb wax oil, so that it can use the principle of siphon action to continuously suck up the melted wax around it as fuel when it is ignited. If the cotton thread as a wick does not fully absorb wax oil, when it is lit, it can only burn the cotton thread itself, and the subsequent fuel supply will be gone, which will naturally lead to the phenomenon that candles cannot be lit.