> On a good day I can work even 12h+<p>I'd wager that your _good days_ are often preceded by a good night's sleep, if not good eating habits and exercise. For over a decade I believed that I couldn't muster more than about 4 hours of focused, creative productivity in any given day. I'd try to plan all of the most demanding work in the first hours of the day, knowing that after lunch I would lose most of my motivation and focus. I was overweight, malnourished, and prone to all kinds of mental disorders (depression, anxiety, anger). At some point I finally had enough, and started on a journey that has brought me to the happiest, most productive years of my life.<p>Get good sleep every single day -- everybody's a bit different in this regard, but there's tons of information out there on how you can achieve this.<p>Eat well -- again, everybody's a bit different, but for me this involves a low carb, high protein diet and intermittent fasting (no breakfast, and eat lunch and dinner within a 6 hour window). No junk food, soft drinks, sweets, etc. I find the trend among scrum masters bringing snacks, treats, cakes, etc., to meetings (planning, refinement, retros, etc.,) totally counter-productive!<p>Get some exercise -- if the local gym or sports club isn't for you, get some kettle bells, or walk or cycle to work, etc. You don't have to run 5k every day (or ever!), but you do need some robust exercise on a regular basis, even if it's 5 minutes with a pair of kettle bells, particularly if most of your days are spent glued to a desk.<p>I would say address these issues first (if they apply to you), and then revisit your view on whether 8 hours of problem solving is feasible on a daily basis.