I can't capture anything
probably because that would be capturing your king, if your pieces could capture your king then you could just capture your king and either 1. Have no way of losing 2. Instantly lose 3. Instantly draw. 4. Turn it into a different chess variant where all your pieces have to be captured for you to lose. 1 and 3 would be unfair if one player is winning and the other just captures their own king to prevent the winning player from winning. 4 would be slightly unfair because if you're about to play checkmate your opponent can just capture their king and change the win condition. 2 is just resigning.