What causes paint runs?

Paint runs are typically caused by applying too much paint at once, either due to overloading the brush or roller or using a paint that is too thin. Inadequate surface preparation, such as not cleaning or priming the surface properly, can also contribute. Additionally, painting in high humidity or at temperatures that are too low may prevent the paint from adhering properly, leading to drips. Finally, failing to maintain a consistent, even stroke while painting can exacerbate the issue.