Loss is loss, and blessing is blessing. In fact, I don't think there is a necessary connection between the two. Every cloud has a ray of hope, not luck, but hard work, and the transformation between loss and happiness is also based on personal summary and learning of failure, but it is not a kind of dumb luck as some people think.
I think, if you want to say that losing is a blessing, you should think about it. Are you just comforting yourself with this sentence, or have you really summed up any experience in this lesson? Have you really learned anything? Will you learn a lesson to ensure that you won't make mistakes again? Can you prevent similar things from happening? If you say you can't do it, there's no need to say such things again and comfort yourself.
Don't always use "losing is a blessing" to find too many gorgeous excuses for your careless failure, and you can't always use it as an antidote to comfort yourself after being trapped, so as to escape the naked cruel reality. Loss is loss, and blessing is blessing. There has never been a reciprocal relationship between them. Only if you really learn something from your losses and mistakes, then your losses are worth it.