Passage Summary: The biggest software customers won't buy anything that is expensive to train staff on. Since memorizing new commands is expensive, successful software cannot use them.

Conclusion: To achieve commercial success, software must not require users to learn and remember unfamiliar commands.

Reasoning: The main buyers of software avoid products with high training costs, and software that uses unfamiliar commands is known to be expensive to teach.

Analysis: The argument identifies a specific group (prime purchasers) and their deal-breakers (high training costs/unfamiliar commands). However, it concludes that *any* successful software must avoid these commands, assuming that commercial success is entirely dependent on these prime purchasers. To bridge this gap, we need an assumption that links 'commercial success' directly to the 'prime purchasers.' Look for an answer that guarantees that a software package cannot be successful unless it appeals to these specific high-volume buyers.