While fans love to debate about which Doctor Who companion is the best of the bunch, one thing that can't be argued is that it must be a tough position to be in.
Just think about it: you're an ordinary human, intelligent enough - but no rocket scientist. Then all of a sudden, you're thrust into a world of time travel, parallel worlds, moving statues and space rhinos, travelling with a grumpy old Time Lord who can't stay still for five seconds, someone who attracts danger like it's going out of fashion. The sheer stress of it all would prompt most of us to tap out after a single adventure.
And yet, despite how difficult it must be to keep up with (and impress) the Doctor, the show's various companions have had plenty of shining moments over the years, and in particular, they've made lots of decisions that prove how resourceful, brave, quick-witted and intelligent they can truly be.
To quote Missy, the Doctor's friends are more than just disposable functions like "exposition" and "comic relief" - they also have their moments of genius thinking too.