Something that happens in the plot that is highly unlikely to happen, though still technically possible.
Different from plot hole as a plot hole is something that should be impossible to happen.
A scene featuring Q giving 007 his gadgets is a staple of James Bond films.
Now imagine if the film did not feature this and we see 007 using a never-before-seen gadget to get out of a tight situation. This would be a plot contrivance, as the audience would have zero reason to believe that 007 would have a gadget of this kind, though him having this gadget is still technically not impossible, preventing it from being a plot hole.
Someone who jumps from one relationship immediately into another one.
Serial monogamists can not stand to be alone and often suffer from vast commitment and insecurity issues.
Because they jump into relationships immediately after the previous one has ended, serial monogamists typically don't take the time to reflect on their behavior or why their previous relationships failed; thus, they end up making the same relationship mistakes over and over again.
Person 1: Damn, Dustin already has a new girlfriend?! It's only been two weeks since he broke up with his fiance! I think he's a sociopath.