Should I use unique or generic discount codes?

I've been running my Shopify store for two years now, and discount codes have always been a bit of a mystery. Initially, I was using the same old 'WELCOME10' code for everyone, thinking it was a simple way to attract customers. But lately, I've noticed something troubling. My conversion rates aren't improving, and I feel like I'm just giving away margin without any strategic benefit. Some visitors seem price-sensitive and need that extra nudge, while others were ready to buy anyway. I'm starting to realize that a one-size-fits-all approach to discounting is probably costing me money. I want a smarter way to offer discounts—something that feels personalized, creates genuine urgency, and doesn't just train customers to wait for generic codes. I've heard about unique, time-limited codes, but I'm not sure how to implement them effectively without making my store look like a discount bazaar. My goal is to convert more of those hesitant browsers into actual buyers, not just give away unnecessary margins to everyone who lands on my site.