Most things can be avoided with proper husbandry, in this case the topic was humidity issues.

With humidity is a vast array of possible issues, primarily related to over or underhydration and disease. With too high of a humidity for a reptile you are saturating their lungs with too much water. This can lead to resporatory infection as well as dry drowning. Bacteria will spread rapidly through their lung tissue and lead to RI. If the humidity is too high their environment will begin to grow mold, mildew, and propogate bacteria. All of which is potentially fatal to the animal.

Too low of a humidity dries out their lung tissue and generates stress on the animal, their immune system will begin to fail and bacteria which is normally kept in check will be able to propogate, leading to RI.

In general there is a band of safe temperatures and humidities for the animal, and if this environment is not met, its immune system may fail, which leads to all kinds of health issues.