Doing only one form of training (the opposite of cross training) is like only reading certain words. Eventually you will be able to read those words very quickly whenever you see them. But you will not be getting any smarter or better able to read.
Life is cross training. Mowing the yard isn’t like trimming the hedge. Vacuuming the carpet isn’t like painting the ceiling. So, as in life, you should experience different forms of exercise to improve how you are living and live how you are improving. I really wish Confucius had said that last one. I really do.