Yes, switching between development and sales/marketing is probably the hardest aspect for me.

Most years I have a booth at an industry trade show. For a couple of weeks preparing for it, the week during the show, and a couple of weeks after that, following up with potential customers I met at there, I find it virtually impossible to get an development done.

Also, onboarding new customers with my software is usually labor-intensive. So that also takes time from development.