[pwatsonwailes]

Light collection. You want to observe one point for a really long time so you get a really good understanding of where the light is coming from, the properties of that light, and its behavioural patterns.

A lot of the detection is statistics around signals, so the better (read more thorough and coherent) your data (observations of changes in light), the more confidence you can have in your conclusions around what's causing the changes (planets with different atmospheres, different positions, different sizes and compositions etc...).