There are three things I learned from loosing, ie. taking losses, sometimes large losses.
1. Personality Fit - I realized what kind of trading style fits my personality, to what extent am I comfortable taking losses. That is when I became damn sure, that it has to be scalping/Intraday trading for me. I cannot think of overnight positions and managing those positions first thing in the morning. I also realized I do not like taking losses once the trade moves in my favor.
2. High Probability Set-ups - Now this one, is learnt better when losses happen consistently in certain set ups, for me it was Mean Reversion Trades + Scaling-in which used to cause disasters. I thought about it and found quite a few solutions to the problem. Usually if a set up is consistently failing, the reverse of that should be profitable, and that worked for me. I also realized the potential risks of averaging down, and the context in which it works.
3. Money/Profits are fungible - This one becomes relevant when you make up the losses that you made. The whole process of loosing and then making it up, gives you a sense of confidence, it also helps you compare and contrast your own approach to trading then and now. Lastly, It makes you more open to taking defined risks.
So here's my thank you to 'Losses' that I made. I am glad you came.