Why did we cut both segments of DNA with the same restriction enzyme?

To explain why we cut both segments of DNA with the same restriction enzyme, I need to explain first what is it used for.

In cloning, we want to insert a gene into a plasmid, which is inside a bacteria and when she multiplies so does the gene.

To insert that gene we first cut him out from a DNA sequence, so To do that we use a restriction enzyme.

Meanwhile, in the plasmid, we also have to make a cut to be able to insert the gene and that will also be done with a restriction enzyme.

This restriction enzyme needs to be the same one that cut the gene. the enzyme recognizes specific sites in DNA, so the plasmid will have ends that will match the gene's ends.

The answer: we cut with the same restriction enzyme to have matching ends when we join both segments.