[smtlaissezfaire]

Usually several factors go into being focused (not necessarily ranked in order):

* Determination. How much do I care about this feature / bug fix?

* Long blocks of quiet. No distractions. This is usually why late at night works really well for me (no interruptions for meals, no emails, etc).

* Interesting factor. Doing drudge work is highly unmotivating. Using a new technology or building something I consider cool (say, a compiler) is tons of fun and I can't rip myself away from it.

[smtlaissezfaire]

Also, forgot to mention sleep. Being well rested always helps - the opposite, being quite tired - leads me to have a hard time focusing.