Simple -- from whose perspective?

"Just keep it simple" -- we sometimes hear this. But from whose perspective?

• Legal/IP
• Management
• IT
• Financial
• R&D
• Security
• Sustaining engineering
• Purchasing
• Manufacturing
• Quality
• Sales/Marketing
• Customer support
• End User/Customer

How do we prioritize simplicity for the above list?

Hint, the one at the bottom is probably the most important. Do you constantly keep your customers in mind as you make decisions? "Customer" may include multiple from the above list.