I had to think a little while about this quote and what it meant. The way I interpret it is as a warning: If you spend too much time focusing on the details (the sesame seeds), you can sometimes lose sight of the bigger picture (the watermelon).
I’m not a fan of sesame seeds on hamburger buns or any other place (are there any other uses for sesame seeds?), so I’ll probably never spend much time picking them up. Besides, if there’s a watermelon in front of me, I guarantee you that thing will be getting my full and undivided attention!