Fly/go off at a tangent phrase
A tangent is a straight line that touches the outside of a curve but does not cross it.
To suddenly move away from the main topic you are addressing or discussing and to think or talk about something else.
When the lecturer was talking about maths, he went off at a tangent and narrated his adventures in Africa.
So far, he has gone off at a tangent two times in this speech. If he does it one more time, I will quit.
The verb "go/fly" must be conjugated according to its tense.
This phrase dates from the second half of 1700s.
Rainy, wet weather
It has been raining for hours, it is the season of lovely weather for ducks after all.