My experience at Gnip has tested me in uncountable ways. From technical capabilities, leadership, and work-life balance, to trouble sleeping due to inability to turn my brain off at night as I churn on our challenges. What I've resolved as the most important thing for me to master in order to make Gnip successful, is my ability to stay on my game despite at least one bummer in the mix at every moment.
Staying positive is the only way to make this game work. When you are in a leadership role at a startup, you are responsible for driving a team with constant impossibility flowing around you.
At a talk he gave last night, Brad Feld, summarized this notion succinctly. To paraphrase, "every single day, there is something going on in my purview that is absolutely abysmal. Deriving energy and passion from it, and, more importantly, the overwhelming amount of positive events, people, projects that comprise the day, is the only way to make it work." It's a very "zen"-like perspective, and one I'm refining and fostering for myself.
If you need day-to-day balance in time, focus, and energy, startups likely aren't for you. You have to find consistency in chaos, clarity in mud, and calm in storms.