Stacks and Queues are "Restricted" data structures. They don't allow you to access elements in the middle. They are designed for specific data flow patterns.
Think of a stack of plates. You can only add/remove from the top.
Think of a line at a grocery store. The first person to join is the first person served.
Q: "How can you implement a Queue using only two Stacks?"
Architect Answer: "You use one stack for 入队 (Enqueue) and one for 出队 (Dequeue). When you want to dequeue, and the 'Dequeue Stack' is empty, you pop everything from the 'Enqueue Stack' and push it into the 'Dequeue Stack'. This reverses the order, effectively turning LIFO into FIFO. This is a common logic test that evaluates your understanding of data flow manipulation."