When I was pregnant with DS (now 3) I worked as an office and site cleaner for a water company, cleaning their prefabricated/portable offices and canteens on sites around the city.
That was difficult as i'd have to clean around the office workers as they sat at their desks, one used to complain whenever I mopped or wiped near his desk despite insisting that I did.
I got a telling off for not dusting on top of the paper towel in the mens loos despite not being able to reach it (I'm 5ft 2) without dragging a chair in from another office and standing on it, not at all safe for a heavily pregnant woman.
The construction workers used to trapse thick mud around the canteen floor as I mopped so I'd end up doing it 5+ times and it still never being good enough.
"You're using too much water" to then "You're not using enough"
The men used to leave the toilet bowls in a disgusting stage despite there having a toilet brush right next to it.
Then there was the gym, my last place, I was expected to deep clean the entire gym and changing rooms within 4 hours single handedly. The manager would follow me about saying it needed to be better. The full time cleaners all quit and I was expected to do their work on top of mine. It was just impossible.
I agree with PP who said that people assume cleaning is an easy job to take up when you're desperate, I certainly felt that way but would never delude myself into doing it again because the reality is very different 
I'm a bit jealous of those who can clean to a professional standard effortlessly.