There is much in life that is open to doubt. Ordinarily, we confine our doubts to specific questions; though we may doubt particular beliefs and ideas, we generally take it for granted that the majority of our beliefs are accurate.
Philosophical scepticism, unlike ordinary scepticism, doubts whole categories of beliefs. Most influential has been external-world scepticism, which doubts the existence of the physical world around us.
There are several different sceptical arguments, and a number of responses to scepticism, available. The problem of dismissing scepticism and vindicating common beliefs remains a live issue in philosophy, however.