What if I just can’t seem to focus during deep work?

Hi! Good day to you! Thank you for the question. As four me I suppose that I can’t focus on work, if I don’t feel that my previous effort was rewarded enough. I’m so sorry for myself – “I have worked so hard I deserve some rest and fun”. If it’s true for you – try to get up earlier and do everything what you like (browsing, posting, watching, reading) before the working day would start. Hope it will help! Have a good day!

Practice, practice, and yep practice. Maybe you're picking too long of a time, try with a shorter time before you take a short break. During your break don't do anything meant to be distracting like social media or entertainment. Walk around for 5 mins, do 10 push-ups, brush your teeth, look up a word in a dictionary that you just came across. Reassess your goal behind the deep work, make it into an affirmation. Also perhaps you're in a busy or cluttered area. Clean the space or try using the library. I don't use them but noise canceling headphones do some people wonders!

You have to cut your trigger and think about the work only
Focus on your goal of your deep work , why you are working deeply !