You have got to be able to counter their strategy.
Making bad moves or playing a really good/lucky opponent, or nor practicing.
The sister devised a plan to beat her opponent at chess.
A good chess player thinks about the game he is playing. A plan. A good chess player thinks about the plan he or she has formulated to attack the opponent. Too many players play without a plan on what to do and how to do it. They just move pieces with no thought about setting up the opponent for the kill. This requires thinking several moves ahead of the one about to be made. For example, a good player might notice that the opponent's King is in danger of a back rank mate, but that a piece of the opponent blocks the way. The good player figures out a way to capture or get the blocking piece to move out of the way. The plan might require making at least two moves to do this but if successful in getting the blocking piece out of the way, the opponent's King is mated.
You can cheat in chess by installing a good chess game in PC. Then make the move opponent makes in the chess game installed in the PC. Then see what move computer makes and do it in the online game.
The sister devised a plan to beat her opponent at Chess.
The answer to your question is yes and no. Yes if you mean to sacrifice it in means of winning material of checkmating your opponent... no to anything else.
A good chess website is ChessKid
The London System is a solid opening strategy in chess that is popular among players of all levels. It is known for its simplicity and flexibility, making it a good choice for beginners and experienced players alike.
Be VERY good at chess.
No, Bobby Fischer did not invent chess. He was a grandmaster, a very good chess player, but did not invent chess.
A good alternative to Chess.com for playing online chess is lichess.org.
When you beat someone in a chess game, you want to be polite. You should always say "good game" and shake hands with your opponent after every game, regardless of the results. And if you want, you can compliment them on their playing, and even point out a few moves you really liked, or think they could improved on.