Startup founders have too many hats to wear (unless they get huge VC funding up front and can afford to hire many people early on). You can't just focus on one or two things and hope to have a successful startup. There are a dozen 'critical' functions that must be addressed.

The trick is to not try and do all those things every day. Pick one or two things to focus on for a day or two. Then context switch to something else that is critical and focus on that exclusively for at least half a day. Trying to context switch dozens of times every single day just doesn't work.