What can happen to a phone if you replace parts on it and you remove/connect ribbons while the phone is on? (Iphone 5s)?

What can happen to a phone if you replace parts on it and you remove/connect ribbons while the phone is on? (Iphone 5s)?

At minimum you'll confuse the poor thing. But there's a chance you could get sloppy and short something out or damage the connectors.