Using cardio to lose weight quickly is a common "mistake". Yeah, it's fast, but your body needs strength training. Muscle burns more calories when we're resting, so doing some lifting (even if it doesn't raise your heart rate as much as cardio) is gonna help you burn more fat in the long run than just a 30-min burst of HIIT. And again, too much cardio can backfire and you might mess up your metabolism. Also, don't focus on the scale so much. Weight is just a number and it doesn't take into consideration where it's coming from.