When you learn a certain group of go-to exercises, it's easy to get in the habit of doing them in the same sequence every time so you don't leave one out. If you're constantly doing exercises in the same order, your muscles will become efficient at doing them, and you'll be more likely to reach a plateau. Try mixing your exercises up. One day, start with lunges and bicep curls, and the next workout begin with squats and overhead presses. Varying the sequence will fatigue your muscles in a different order, which will not only be more challenging but will also prevent boredom.