I'm sure you've done them a hundred times before, but we are always able to improve upon ourselves. When we do, we become better, stronger, and build more confidence in our abilities. I personally love Mountain Climbers because they are so great for a shoulders, core, & cardio workout all wrapped into one and it's a bodyweight exercise that you can do anywhere. Give them a shot and modify where needed.
If you start at the beginner level keep progressing, even if it's for a couple reps before returning to your previous mod for the rest, each workout that you have Mountain Climbers in it. You will get stronger the more you try to push yourself farther than you went yesterday.