Before we say anything else, let’s just lay out the ground rule. A good primer is a must-have makeup product. No exceptions. In an ideal world, it would be a regular feature, even on a minimalistic makeup day. For those of you, however, who think of it as an unnecessary prep step to makeup, you might change your mind after you try it. The best way to test primer power is by using it on those heavy events to see if it can carry the burden. If it emerges a winner, you know it’s a keeper. Here are 5 occasions when a primer is non-negotiable.