Whenever a scientist character says that something could "theoretically" have happened, it's a perfect explanation of what actually happened, even if everyone else says how unlikely it is. Similarily, if a scientist character proposes a "theoretical" solution to a problem, it'll always solve the problem, but not without a lot of tension over whether or not it will work.
For a reason as to why "theoretical" explanations and solutions are so often successful, see Gravity Is Only a Theory.
- Sunshine: In a (partial) subversion, the characters pick up a second bomb, purely because they think "two have a better chance than one". Their computer simulation even shows that what exactly will happen is completely unknowable. As it turns out, they would have been better off if they hadn't risked it.
- Subverted in Back to the Future trilogy: Doc explains that a Temporal Paradox caused by you seeing your time-displaced self could theoretically destroy the universe ("Granted, that's a worst-case scenario. The effects may be limited to just our own galaxy.") When one such paradox actually does occur... all that happens is both people faint on the spot (which he also predicted as a possible outcome). The fainting could just be explained by simple shock, and the fact that Hollywood executives think that all women are prone to fainting.
- A Running Gag in Terminator Genisys has the Guardian using the terminology of "theoretically" for things that really need a definitive explanation. Though Kyle Reese initially is annoyed by it, he eventually picks it up as well.
- Fringe: Walter (as an actual "distinguished" but elderly scientist) does this all the time, with Peter pointing out how crazy it seems.
- Used practically Once an Episode on Eureka. The basic outline for an episode: Some bit of Phlebotinum is threatening the town, So Carter turns to either Henry, Allison, or Nathan (or some combination thereof) for an explanation. Said explanation usually begins with "Well, theoretically..." Carter lampshades this is later seasons with "I hate the word!"
- Star Trek: Every series, every episode. This is prevalent to the point where the Federation hires theoretical scientists as engineers. The TNG Enterprise was largely designed by theoretical physicist Dr. Leah Brahms, who demonstrates a contempt for applied science that's altogether unhealthy for an engineer, to say the least. One fan lambasts her character here.