Patience (also known as solitaire) refers to any card game for one person. There is a wide variety of patience games, most of which involve building cards up (or occasionally down) in sequence. Some patience games mostly require luck rather than skill, but some require good judgement in deciding where to place the cards, and in some, where all the cards are visible from the start, thinking ahead is required to work out a winning strategy or determine that none exists. The two most commonly played patience games (both of which also exist as computer games) are Demon (also known as Canfield) and Klondike (the Solitaire game for Windows).