> For the complete documentation index, see [llms.txt](https://akm5630.gitbook.io/understanding-causal-inference/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://akm5630.gitbook.io/understanding-causal-inference/limitations-of-causal-inference/fundamental-problem-of-causal-inference.md).

# Fundamental Problem of Causal Inference

Causal Inference has a missing data problem. We cannot observe both the potential outcomes, we only observe one. **This is also considered as a Fundamental Problem of Causal Inference.**

**Example:** In the case of a medical procedure, we can only observe when people are given medical treatment or not. We can never observe both.