You can be a queen and a knight ahead and lose the game in one move. Here is the position, and it is the quickest way I know to show a beginner what chess is really about.
7 
2 
e 
g Count the points and Black is winning by miles. Count the black king’s escape squares and Black is losing, because there are none. Whenever those two counts disagree, the escape squares win.
That is the objective, stated in one line by Article 1.2 of the FIDE Laws: attack the opponent’s king so that the opponent has no legal move to answer with. Every capture, every pawn push, every manoeuvre you will ever play is a way of getting to that, and nothing else counts at the end.
So why does everybody talk about winning material?
Because it is the reliable route. Being a rook up does not end the game, but it means you can trade everything off and still have a rook and a king against a bare king, and that ending is a forced mate in a dozen moves or so. Material is the currency you exchange for a mate later.
That is also why the piece values exist as a rule of thumb and not as a law. Nothing in the FIDE Laws mentions nine points for a queen. The numbers only describe how likely each piece is to help you reach the king.
The other ways the point goes to you
Most games between strong players never reach mate at all. Your opponent resigns, because a grandmaster who is a piece down with nothing to show for it can see the rest of the film. Or the flag falls and the clock decides it, so long as you still hold enough material to mate with. Or, rarely, a rules penalty ends it.
None of that changes the objective. Resignation is just an admission that the mate is coming, and it is the same admission chess makes when it stops the game at checkmate instead of letting anyone capture a king.
Start with the picture, not the arithmetic. Set up a few mate-in-one positions, count the king’s squares before you count the pieces, and read what checkmate actually is next, because telling it apart from stalemate is the thing that otherwise costs you half a point.
Then put the position at the top of this page back on a board and look at it once more. Black has the queen. Black has the knight. Black has nowhere to put the king.