They are the keys to improved performance. Many constraints are merely consequences of choices you've made. You may view some constraints, such as the weather, as uncontrollable. Yet even then, the risk is often controllable over the longer term. It could mean product or geographical diversification.
Assumptions are often unstated and overlooked.
Test all assumptions and be sure they are valid. Often assumptions are made based upon the best information available and then somehow they become rigid rules. If you want to thrive and prosper, focus on being the best you can be. Challenge your staff to find ways to break through old barriers. They will become leaders - people of vision who want to be out front.