When it cuts it leaves sticky ends or un-base paired single stranded regions on each end of the part its cut and that's just a property of many restriction enzymes; not all, some cut blunt,just right down the middle.
If I cut both the plasmid and my DNA of interest with the same restriction enzyme I'm going to end up with the same sticky ends on both molecules.
如果用同一种限制性内切酶,来切割质粒和我感兴趣的DNA,在两个分子上就能得到同样的粘性末端
生物医学工程探索课程节选 : 耶鲁公开课
3
If you cut and you open up a segment of DNA then you've left these sticky ends, for example and these sticky ends are capable of recognizing each other by the process of hybridization.