Others never do things at the same times from one day to the next. Others seem to do fine no matter where they are, or with whom. Others howl as soon as they're unhappy. Others can sleep through thunderstorms. All these things together make up your baby's temperament.
Some combinations are easier to live with than others.
Easy babies are somewhat active and predictable. They adapt easily to change, and are usually happy. Difficult babies tend to be unpredictable. They withdraw from new situations, adapt slowly to change, and react very strongly. Baby is not difficult on purpose, and is not a bad baby.