Great question:

Even though gene expression can be random, especially with low molecule numbers, it's pretty rare for fatal mutations to happen because our bodies have several safeguards in place. The genetic code has built-in redundancy, so not every mutation causes a problem. Cells also have error correction mechanisms to fix mutations when they occur. Plus, proteins are often able to function even if there’s a small change, and our gene regulatory networks are designed to be robust against fluctuations. On top of that, natural selection weeds out harmful mutations over time, and essential genes are usually well-protected, making sure critical functions are maintained.

The answer is more complex, deep and nuanced than this at the biological level as biological systems are inherently dynamic.

Hope this helps.