In the UK we have a criminal legal system which requires the burden of proof to be “beyond reasonable doubt” – should any doubt be present then the defendant should be acquitted of any charges. You already knew that.
The way the system works is a witness will be questioned by their own counsel and then cross examined by the other side. The idea here of course is to determine the facts of the case and convince the jury (if present) that something did or didn’t happen, how it did or didn’t happen and to prove or disprove the charge. The questions can often be difficult and since most barristers are cunning, the questions will also be worded and crafted in such a way as to get the answer the particular barrister wants. But you already knew that too.
It is quite fun to watch when this kind of thing happens. You can see how answers are manipulated and in many cases the witness will become frustrated, making them even easier to question. This is fine if the witness is a horrible criminal – you want to see them have a hard time – but what if the witness is the victim or someone who is vulnerable? Fine if they’re a hardcore robber but what if they are a young rape victim?