I don't regret about losses nor pay attention to reasons of loss of a particular trades. Instead I try achieve some statistical improvements in my losing trades like to decrease max drawdown, variability of loss (obviously losing stop loss setting) or average loss per trade.
To handle losses I always use tight stop loss. I prefer many small losses over 1-2 losses with big impact on my account, because it's is mentally harder to cope with big unexpected loss. We have to consider emotional factor in trading as well.
Those who claim they never face a trading loss simply do not trade. A loss here and there is normal in every trading strategy and nothing is 100%. A trading loss should never break your account performance and dealing with a trading loss the proper way is a very important step or everyone who aspires to become a real trader.
There are different steps to take after a loss and I think one of the most important one is to step away for a bit and calm down if the loss has caused you to become emotional.
Once you have regained your composure sit down and analyze your loss, understand why you lost and learn how to reduce or eliminate what caused your loss. A loss is only bad if you refuse to learn from it.