The ability to concentrate is definitely not what defines me. I could get distracted by a pen sitting on my desk in like 3 minutes.
My work environnement doesn't help either, as we're in open space, and must stay on top of the requests arriving in the chat (hangouts).
Doing sprints on short time periods (eg. with the pomodoro technique) are great for me, but I've found that such techniques take long to prepare (splitting things in small subtasks, etc), and it is inefficient when you need to be multitasking. Focusing only on one task is great for this task, but definitely bad for all other tasks that you're putting on hold.

The way I do multitasking is with tmux usually. I keep one "workspace" per task, and split the window when needed. I work on the task a bit, then switch. By keeping all the windows open its easier to get back the context on thos task when, for example, your run `history` or check the hostnames of the servers you're logged into.

My main struggle then is not to forget about a task... using a ~/.todo file is not enough...