I've posted a question on a forum asking about the way I was using a technology. I asked if my way was the best way. So, someone has answered me: "It's certainly not a given.". I'm not sure about the meaning of this expression. What does it exactly stand for? Thanks.
"It's certainly not a given" is a rather indirect way of saying that arguments exist against your position. If something is a given, it is not debatable and it is pretty much universally accepted.
A given, as a noun, means approximately 'an unarguable fact, similar to an axiom'. Rather to my surprise, it was not in the first two dictionaries I tried; but the related senses, at a given time and date (you can calculate your position from the stars) meaning 'at any particular time, not dependent on contingencies'', and Given that x is 17, calculate y (so there is no point saying "Actually x is not 17"; it is unarguable, similar to an axiom) are universally known.