I just heard someone say that when your mind is telling you you’re done, you’re only 40% done. We have all experienced this in a workout. You are doing a 5 round workout and in round 3 your mind is telling you 
that you cannot go on, that there is nothing left. Yet you finish the workout. We have all seen the poster of the guy digging the tunnel and he is quitting but he can’t see that he right about to break through to the other side with one more shovel full of dirt.
We know that we can learn to overcome this voice with practice. If we continue push past our limits we find that we create new limits. If we expect more of ourselves, we get more from ourselves. The difficulty here is that pushing our limits is uncomfortable: it downright sucks. The harder you push, the harder life pushes back. It takes mental and physical strength. The key here, just like in the gym, is consistency and progressive overload.
Train your mindset consistently. Try to be uncomfortable every day. However, what was uncomfortable yesterday is easy today so you have to keep pushing the boundaries. It is easy to trick yourself by doing something that once was hard for you but now is relatively easy. Don’t fall into that trap. Keep pushing.
Get out of your comfort zone today.