Titanium tends to flex easily. It is a little more elastic than steel. As you put it through stress cycles where it flexes it will either become brittle and crack or bend permanently. If it has an area that acts as a stress riser it is likely to crack. Take a material science course. It's very interesting. It's been too many years since I took mine.
well, if you mean 'will hucking stairs on a Ti road bike be bad for it?' yes, it can break and bend like any other material. It tends to bend a lot before it cracks though, and can be bent back easily enough. Bend it back and forward a lot of times and it will break. Ti is more suceptable to notch type failures than many other metals. This means that a deep scratch becomes a serious stress riser and is likely to be a failure point.