Continual perceptual processing, such as required for decisions that necessitate the accumulation of evidence over time, is essential for efficient behavior. The behavior emerging from a wide range of such decisions turns out to be well-described by a surprisingly simple model family - the diffusion decision model. Taking a decision-theoretical perspective, I will discuss why diffusion models might have this property across perceptual and value-based decisions. I furthermore will highlight scenarios in which such simple models will become insufficient.