Gene drives are posited as a method for eradicating troublesome species such as mosquitoes. Release a bunch of males (who don't typically bite) with a lethal edited gene, and populations should dwindle rapidly, without contaminating the genes of the species.
Unfortunately, as is often the case with these things, life, uh, finds a way. A few percent of the hybrid offspring managed to survive the terminator gene long enough to reproduce, meaning that transgenes are now permanently embedded within the population, and will likely spread into other populations and subspecies.
This means that a permanent resistance may have been introduced, frustrating future opportunities. Crucially, such transgenes might be introduced to other species, such as during fluid transfer between mosquitoes and the organisms that they feed upon.
We have a very poor awareness of potential long term effects of transgenes, or if they may be more easily exchanged via horizontal transfer than regular genes. In any case, this case illustrates that geneticists need to be far more careful in future when messing around with complex systems. Nature can make an incredible ally, but it's a very elusive opponent.