Everyone who designs electronics for use in a marine environment considers the effects of salt spray and humidity - and well they should, they're horrible! But many electronic devices may encounter lesser, but still potentially damaging, chemical challenges. Human (and animal) breath is humid, and slightly acidic. Kitchen and other domestic environments contain mildly corrosive fumes of various types (bleach, disinfectant, cooking fumes of various sorts, and oils and spirits) - none of which is very damaging but we should not assume that our circuits are going to spend their entire lives in perfectly protected safety. Designers should always consider the environmental challenges their circuits will encounter and, where economically possible, design to minimize any potential damage.
Electrostatic damage (ESD) is one stress mechanism which we are continually warned about, but still regularly overlook. After being built in a factory where every care is taken to eliminate ESD during manufacture, many PCBs are used in systems without adequate protection from the ESD induced by normal handling. Adequate protection is not hard, but it may add a few pennies to the cost and so is omitted. That can be poor economy. Part of every design should be an assessment of what ESD protection is necessary for the system electronics in the most extreme conditions of normal use, and its implementation.
Overvoltage is another factor. Few people expect semiconductors or capacitors, to survive gross overvoltage, but it is common to see high value resistors subjected to voltages massively larger than the absolute maximum on their data sheet. The problem is that if their resistance is high enough they don't get warm - but they may suffer from microscopic internal arcing and slowly drift out of specification, and eventually short-circuit. Large wire-ended resistors usually have breakdown voltages of many hundreds of volts so the problem was uncommon in the past, but today's tiny surface-mount resistors may have breakdown voltages below 30 V and be quite vulnerable to overvoltage.