Fox One

There's a fair whack of wisdom to be found in Skins.
In modern combat aviation (not that I know much about it) the term 'lock-on' refers to the process where-by one aircraft's fire control computer acquires a possible shooting solution on another aircraft.  I love Wikipedia.  The term was used in world war two to describe the situation where a fighter pilot would focus on one aircraft to the extent that he would be oblivious to other threats or their proximity to potential threats, such as the ground.
I use the term 'locked-on' to describe a pattern of circular thinking that tends to cycle unhelpful and unfocused thoughts around until I'm obsessed with them to the exclusion of all else.  At the time the thoughts don't seem unhelpful, they seem ground-breaking, philosophical and unquestionably true.  At their worst they make me want to die, at their best they allow me the clarity to make completely unworkable plans with unlikely and impossible outcomes.

The difference between the modern definition of 'lock-on' and the second world war definition is one of control.