English is the hardest language to learn. We have homophones (flaw and floor) and homographs (wind-up wind chimes). We have impossible spellings and silent letters (Siobhan Marjoribanks, Knight Pneumatics Ltd, Azalea Rd, Loughborough). We have so many irregular verbs that it's difficult to spot the regular ones (find/found; bind/bound; blind/blinded). We have secret inflections that we only use on special occasions (to whom it may concern, as it were) and then after all that you have to learn the idioms.
An idiom is a colloquial metaphor. We all agree on them and we've all learned them but they are figurative and obscure rather than literal or transparent. Here are a few imaginary places that things can go to. I have no doubt that there are many more and I have deliberately omitted the dirty ones.
Go south / go tits up / go pear shaped / go off the rails - deteriorate
Go round the houses - take a circuitous route
Go off the deep end / go off on one - have an emotional outburst
Go over the top - do something to outrageous extreme
Go underground / go off-grid - hide
Go on a mission - do something urgently
Go mental at - to remonstrate with
Go for a burton - go unexpectedly missing
Richard "Never go Full Retard" B