A second hand bike I recently acquired has proved to be a bit over-sized for me. The reach is a bit too much so I decided to fit an adjustable handlebar stem today. To my horror, I discovered the old stem was cracked almost from side to side directly underneath where the handlebars attach. Basically, unless you had a swan neck or turned the bike upside down to inspect it you would not spot it. It was literally minutes from failing, which had it done so on a fast decent for example would have been very painful
So the lesson is, do turn your bike upside down and check for cracks in the frame, forks, seat post and stem regularly folks!!