Getting your partner an engagement ring is highly stressful. First of all, it's one of the most expensive material purchases you will make as a couple. I've heard somebody say they wouldn't even want it if the ring isn't worth three months' income. With that in mind, there's no real way of knowing whether your partner will like the ring you picked out. Sure, they might tell you their taste in jewelry, but until they see it with their own two eyes, it's such a gamble.
Even if you don't know exactly what to get your partner for an engagement ring, you intuitively know what not to get them. A gaudy ring that looks like it could be purchased at a Charming Charlies is a huge no-no. Unfortunately, one guy did not know that rule and bought his girlfriend a gaudy ring with a giant amber heart on it. God bless the poor woman who posted it online asking for advice on how to tell him the truth about his choice.