I wouldn't say it's you. In this instance Dave simply has more enthusiasm. I love my job equally as Dave I'm sure but also can struggle with motivation, particularly on the first day back after the weekend and we've just had 4 days off. We've 4 more this weekend coming so I'll be the same next week. But that's life, us, who we are. Dont beat yourself up about it, you'll only make matters worse. I just like to look forward to the end of the day and hoping I achieve my daily targets, so long as I dont set them too high.