You know your undertone. Cool, or warm, or somewhere in between. The question is what you actually do with that on an ordinary morning when you're standing in front of your closet holding two tops that both seem fine.
The answer depends less on the colors than on how you process information. And S vs. N is one of the clearest differences I've seen.
If you have a Sensing preference (S):
You work with what's in front of you. Abstract principles don't stick as reliably as concrete reference points, so the most useful undertone check is a physical one. You probably already have at least one piece in your wardrobe that you know works. Use it. Hold the new item next to something confirmed, and let your eye tell you whether it reads the same or pulls differently. You're not analyzing the theory. You're observing a direct comparison. That's your data.
If you have an Intuitive preference (N):
You're more likely to work from the principle. Once you understand that your undertone describes where your coloring sits on the warm-cool spectrum, you can apply that framework to evaluate a new color before you even hold it up. The question you're asking is: does this color pull yellow-gold, or does it pull blue-violet? You'll often make that call quickly and trust it, because you're pattern-matching against a concept you've already internalized.
Same attribute. Same Tuesday morning. Two completely different access points — and both of them valid.
Which one sounds more like how you actually navigate a color decision? Or do you find yourself switching depending on the day?