You don't have to go hard every day. But sometimes, you have to go as hard as you can.
That doesn't mean you need fancy equipment or a complicated workout plan. The "fun" way to do it is with intervals; and if you can rotate between types of exercise, but still maintain a high intensity, it will feel like a game you play against yourself.
For example, it's more fun to do a hard circuit of squats, pushups and sprints than to do sprints alone, and you'll get the same benefits.
Push yourself.