But when you're debugging, you know where to focus your efforts. If 95% of your code touches the other 5%, then that 5% is probably pretty important and useful

But when you're debugging, you know where to focus your efforts. If 95% of your code touches the other 5%, then that 5% is probably pretty important and useful and hopefully fast. Spending some extra time to verify safety in exchange for speed/control is a small price to pay, and will pay dividends from the other 95% of code that doesn't have to be inspected so closely.