What does it mean that typing adds constraints that prevent errors?

Assigning types to objects restricts what operations make sense on them.

Example: You have a field in your project tracker labeled 'priority.' Without a type constraint, someone enters 'high,' another enters '1,' a third enters 'ASAP,' and a fourth enters the color red. The field becomes useless — not because people are careless, but because unconstrained fields accept anything, including nonsense. Add a type (e.g., enum: critical | high | medium | low) and the field rejects invalid inputs before they pollute your system.

Try this: Pick one field, category, or label you use regularly in your work or personal system — a task status, a priority level, a project phase, a contact type. Write down its current 'type': what values are allowed? If the answer is 'anything,' define a constrained set of 3-5 valid values. Then audit your last 10 entries. How many would have been caught or corrected by the constraint?