This is the complete riddle:
Si no puedes dormir y el sueno deseas, lo vas a conseguir si cuentas ovejas.
This means that if you want to sleep you need to relax your mind. In this way, if you start counting sheep in your mind there will be a point in which you will get to sleep. Is it a trick? Maybe! Because you are playing with your mind until it gets tired. Then you could sleep by counting sheep.
