The Stanford Encyclopedia of Philosophy identifies sense data as what we are directly aware of in perception. Sense data is dependent on the mind and has the properties that perceptually appear to us. Sense data can include elements we are indirectly aware of as well; we can use direct perception and induction to amass indirect data about something. Although indirect perception may not depict a complete understanding, it uses direct perception to give a probable conclusion. 
Sense data is flawed because of the following four objections.
First, the theory of physicalism (the belief that mental states do not exist or can be reduced to physical states) contradicts sense data’s reliance on the brain. Sense data compiles sensory perceptions into brain states, yet brain states are not physical states. As a result, sense data is flawed because it does not conform to the physical nature of this world.
Next, sense data is commonly rejected for epistemological reasons. Relying only on sense-data leaves us vulnerable to believing that the external world may not exist; it primarily relies on direct perception, leaving plenty of room for doubt. Sense data also fails to explain how we can conceive of physical objects without having a direct perception of that object. For example, many people know what a cheetah looks like without actually seeing one in person. This contradicts self data, which states that we can only gain knowledge about a cheetah using our senses.
Third, visual sense data perceptually appear to us, so they must have the sizes, shapes, colors, and other visual components that we perceive in person. These aspects of visual sense data must occupy space, yet there is no explanation for the space that sense data occupies. For example, if one sees a table, then the sense data must be shaped as the person perceived the table. Yet, data is not perceived in shapes, so visual sense data is flawed. 
Lastly, the theory of indeterminacy states that objects can often have indeterminate qualities. If someone cannot perceive an object's qualities with full assurance, then sense data cannot be trusted. Many intricate objects, such as art sculptures, can have indeterminate qualities, reinforcing the notion that sense data is flawed.
Sense data’s over-reliance on human perception causes it to be a fundamentally flawed way of looking at the world.