“Being with my sister who gets angry with the smallest thing was like walking on eggshells.” Literally, walking on eggshells would mean breaking the eggshells and ruining the eggs. When applied to situations in life, walking on eggshells would be like venturing into a hazardous or sensitive situation. It relates to how to deal with people who react rashly and impulsively at the least provocation.
The origin of the idiom "Walking on Eggshells" is not clearly known but is allied to other similar idioms such as “walking on thin ice” or “walking on broken glass”. It may have also evolved from the older idiom “walking on eggs” which presents an equally difficult situation of avoiding damage while walking on a delicate object. May be dubious politicians may have the skill of walking on eggs without damaging them, while dealing with contentious issues.
Any situation which warrants the need for tact as against a confrontation would require the person to walk on eggshells as in the case of a family having a temperamental member who flies into a fit of rage on the slightest whim. Similarly to have an alcoholic partner is like walking on eggshells when he is around. Talking to your friend about her ex-boyfriend after he has ditched her is again a case of walking on eggshells which should be clearly avoided.
The idiom "Walking on Eggshells" implies being extremely careful while broaching certain topics with certain people. In fact, avoiding the likely-to-offend issue altogether as you are bound to destroy eggshells while walking on them. Literally walking on eggshells would expect one to be exceptionally cautious and show considerable restraint while dealing with an already disturbed person in order to avoid conflict of any kind. In order to avoid walking on eggshells, people must take care not to offend a hypersensitive person by asking questions on a volatile topic. In a social or work environment there may be people exploding into volatile behavior at the slightest offense. The best defense against such behavior would be to tread lightly and avoid walking on eggshells.