Chapter 4 is just littered with Trophies/Achievements to earn, and this is another easy one to miss (like all of the Hojo related ones). You’ll have to progress through the Chapter until you return to the Shinra Building to protect Professor Hojo.
You’ll find yourself in the Fusion Chamber where you can interact with many different apparatus, most of which lead to a Trophy/Achievement. For the Of Significant Worth Trophy/Achievement, you’ll need to interact with the fusion chamber itself. At this point, Zack will get locked inside and Hojo will only let you out if you answer a series of questions correctly:
1. A SOLDIER operative like Sephiroth.
2. State-of-the-art science and technology.
3. A person unafraid to challenge Shinra
Answering all of them correctly and satisfying Hojo’s curiosity is enough to have him let Zack out of the fusion chamber and award you with the Of Significant Worth Trophy/Achievement. If you failed in answering any of the questions correctly, be sure to load up your Save (which should be in the same room as you are now).