Why did i find one complete leaf turning yellow

My plant is dark green and one of the bottom leaves was completely yellow. All the other leaves were fine. What causes a single leaf to go yellow. It wasn't dry andcrumbly

How old is it? It happens sometimes..as long as it's just one and doesn't start spreading don't worry about it. If more start showing up you may need to increase your feeding. My mothers yellow and drop leaves regularly because i run them on a low nute regiment so they start eating themselves a little bit.