One pattern I've seen often is neglecting the cost of crossing layers. You'll have some tool or service that is used and then some client code will end up loopi

One pattern I've seen often is neglecting the cost of crossing layers. You'll have some tool or service that is used and then some client code will end up looping through hundreds or thousands of uses of it. Meanwhile, the otherwise negligible setup/teardown costs that come with crossing that layer adds up, and you end up with horrendous performance because of it.