3 is a number of simplicity and engineers use it to count the number of essential questions to ask when deciding to purchase an item. Here they are:
1. How much does it cost?

2. How long will it last?

3. Will it cause me to socialize with people?

The answer to 1. should be very little.

The answer to 2. should be very long.

The answer to 3. should be, “No.”

There is an expanded list we may cover in later posts, but these three pretty much sum it up. The implications are simple. The answers should be straight forward. No whimpy, “Will I feel better with this item?” If it is needed (which is really the first deal-breaker of a question) then the engineer will work through these three questions.
What could be easier?