Cheap becomes expensive when failure arrives at the worst possible moment.

The saving on a cheap item is collected once. The failure, when it comes, arrives on its own schedule, usually when the thing is most needed and least replaceable, and the cost then includes the disruption rather than just the item. That timing is what makes the arithmetic misleading.

Where failure would be expensive or badly timed, pay for reliability. Where failure would just be mildly annoying, stay cheap. Sort your possessions by the cost of them letting you down.