When I'm feeling strong, I have a propensity to work harder with a notion that it will be beneficial. What sometimes doesn't come to mind is the risk of over-training that causes physical and psychological damage. I have a weekly email calendar reminder and a weekly mobile phone reminder to stay mindful of this risk when pushing myself hard.
I began my practice two years ago at the age of 54 so I am often fired by this desire to make up for lost time by pushing too hard. I'll start to play it safe and mindfully employ certain modifications when aches and pains arise, but inevitably my competitive impatience takes over, and I start pushing too hard again, a little here, a little there. Talking with my instructor is helpful, but it really comes down to me finding the right balance, finding the right path to self-study and serenity.
I play it safe. I've injured myself too many times trying to do something my body isn't prepared to do. I've learned that, at my age (58), it's better to be cautious and be able to continue practice than go over the edge and end up unable to practice for months while a tendon recovers.