How do you explain your multiclass?

I see a lot of posts here about people wanting to multiclass in their games, but what are your in game reasons?

Like for example, my warlock has recently taken a level in sorcerer due to him beginning to absorb his patrons powers.

Edit: this post was more intended for those who want to include flavour to their multiclass. I get people completely remove the whole "classes" idea from their games, I was just trying to create discussion on this idea.